General Description
The MAX7347/MAX7348/MAX7349 I2C interfaced periph-
erals provide microprocessors with management of up to
64 key switches. Key inputs are monitored statically, not
dynamically scanned, to ensure low-EMI operation. The
MAX7347 can monitor up to 24 switches, the MAX7348
can monitor up to 40 switches, and the MAX7349 can
monitor up to 64 switches. The switches can be metallic
or resistive (carbon) up to 1kΩ.
The key controller debounces and maintains a FIFO of
key-press events (including autorepeat, if enabled). An
interrupt (INT) output can be configured to alert key
presses either as they occur, or at maximum rate.
The MAX7348/MAX7349 feature a tone generator to
generate automatic key-click sounds or alarm tones
under processor control.
The sounder frequencies cover the 5th musical octave
(523.25Hz to 987.77Hz), plus seven other musical
notes up to 2637Hz. The output can also be pro-
grammed to be high or low for the sound duration to
operate an electronic sounder, relay, or lamp.
The MAX7347 is offered in 16-pin QSOP and TQFN
packages. The MAX7348 is offered in a 20-pin QSOP
package. The MAX7349 is available in 24-pin QSOP and
TQFN packages. The MAX7347/MAX7348/MAX7349
operate over the -40°C to +125°C temperature range.
Applications
Medical Instruments
Instrumentation Panels
Security and Access
Industrial Controls
Features
♦400kbps, 5.5V-Tolerant 2-Wire Serial Interface
♦2.4V to 3.6V Operation
♦Monitor Up to 64 Keys (MAX7349),
40 Keys (MAX7348), or 24 Keys (MAX7347)
♦FIFO Queues Up to 8 Debounced Key Events
♦Key Debounce Time User Configurable from 9ms
to 40ms
♦Key Autorepeat Rate and Delay User Configurable
♦Low-EMI Design Uses Static Matrix Monitoring
♦Hardware Interrupt on Each Debounced Event or
FIFO Level, or at End of Definable Time Period
♦Up to Six Open-Drain Logic Outputs Available
Capable of Driving LEDs
♦Sounder Output Generates Automatic Key Clicks
♦14 Programmable Musical Sounder Frequencies
♦Continuous or Programmable Sounder Duration
♦Easy Automatic Single-Tone and Dual-Tone Alarm
Sound Generation
♦Four I2C Address Choices
♦Selectable 2-Wire Serial Bus Timeout
♦Under 10µA Shutdown Current
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-3556; Rev 5; 5/07
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-
PACKAGE
PKG
CODE
MAX7347AEE+ -40°C to +125°C 16 QSOP E16-4
MAX7347ATE+ -40°C to +125°C 16 TQFN-EP* T1644-4
MAX7348AEP+ -40°C to +125°C 20 QSOP E20-1
MAX7349AEG+ -40°C to +125°C 24 QSOP E24-1
MAX7349ATG+ -40°C to +125°C 24 TQFN-EP* T2444-4
+
Denotes lead-free package.
*
EP = Exposed paddle.
MAX7349
V+ COL_
SOUNDER
GND
8
SCL
SDA
AD0
ALERT
ROW_
8
PIEZO
TRANSDUCER
SWITCH
ARRAY, UP
TO 64
SWITCHES
INPUT
2.4V TO 3.6V
INT
Typical Application Circuit
Pin Configurations appear at end of data sheet.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
(All voltages referenced to GND.)
V+ ............................................................................-0.3V to +4V
COL2/PORT2–COL7/PORT7 ....................................-0.3V to +4V
SDA, SCL, AD0, ALERT, INT ....................................-0.3V to +6V
All Other Pins................................................-0.3V to (V+ + 0.3V)
DC Current on COL2/PORT2–COL7/PORT7 ......................25mA
DC Current on SOUNDER ................................................±25mA
GND Current .......................................................................80mA
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........666mW
16-Pin TQFN (derate 16.9mW/°C above +70°C).......1349.1mW
20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW
24-Pin QSOP (derate 9.5mW/°C above +70°C)...........761mW
24-Pin TQFN (derate 20.8mW/°C above +70°C).......1666.7mW
Operating Temperature Range (TMIN to TMAX) ...-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(V+ = 2.4V to 3.6V, TA= TMIN to TMAX, unless otherwise noted. Typical values are at V+ = 3.3V, TA= +25°C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Operating Supply Voltage V+ 2.4 3.6 V
Operating Supply Current I+ All key switches open 75 100 µA
Shutdown Supply Current ISH 6.44 10 µA
SOUNDER Output High Voltage VOHBUZ ISOURCE = 10mA V+ -
0.45 V
SOUNDER Output Low Voltage VOLBUZ ISINK = 10mA 0.15 V
SOUNDER Frequency Accuracy TA = +25°C, V+ = 3.3V 1.2 %
Key-Switch Source Current IKEY 28 40 µA
Key-Switch Source Voltage VKEY 0.35 0.65 V
Key-Switch Resistance RKEY (Note 3) 1 kΩ
Startup Time from Shutdown tSTART 57 200 µs
Output Low Voltage
COL2/PORT2 to COL7/PORT7,
INT Output
VOLPORT ISINK = 10mA 0.15 V
Input voltage ≤ V+ -1 +1
Input Leakage Current Alert Input voltage > V+ -5 +5 µA
Input High Voltage ALERT VIH 2.2 V
Input Low Voltage ALERT VIL 0.8 V
SERIAL-INTERFACE SPECIFICATIONS
Serial Bus Timeout tOUT With bus timeout enabled 20 68 ms
Input High Voltage
SDA, SCL, AD0 VIH 2.2 V
Input Low Voltage
SDA, SCL, AD0 VIL 0.6 V
Input voltage ≤ V+ -1 +1
Input Leakage Current
SDA, SCL, AD0 Input voltage > V+ -5 +5 µA
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
_______________________________________________________________________________________ 3
I2C TIMING CHARACTERISTICS
(V+ = 2.4V to 3.6V, TA= TMIN to TMAX, unless otherwise noted. Typical values are at V+ = 3.3V, TA= +25°C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Capacitance
(SCL, SDA, AD0) CIN (Notes 3, 4) 10 pF
With bus timeout enabled 0.05 400
SCL Serial Clock Frequency fSCL With bus timeout disabled 0 400 kHz
Bus Free Time Between a STOP
and a START Condition tBUF 1.3 µs
Hold Time (Repeated) START
Condition tHD
,
STA 0.6 µs
Repeated START Condition
Setup Time tSU
,
STA 0.6 µs
STOP Condition Setup Time tSU
,
STO 0.6 µs
Data Hold Time tHD
,
DAT (Note 5) 0.9 µs
Data Setup Time tSU
,
DAT 100 ns
SCL Clock Low Period tLOW 1.3 µs
SCL Clock High Period tHIGH 0.7 µs
Rise Time of Both SDA and SCL
Signals, Receiving tR(Notes 3, 4) 20 +
0.1Cb300 ns
Fall Time of Both SDA and SCL
Signals, Receiving tF(Notes 3, 4) 20 +
0.1Cb300 ns
Fall Time of SDA Transmitting tF.TX (Notes 3, 6) 20 +
0.1Cb250 ns
Pulse Width of Spike Suppressed tSP (Notes 3, 7) 50 ns
Capacitive Load for Each Bus
Line Cb(Note 3) 400 pF
Note 1: All parameters are tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: All digital inputs at V+ or GND.
Note 3: Guaranteed by design.
Note 4: Cb= total capacitance of one bus line in pF. tRand tFmeasured between 0.8V and 2.1V.
Note 5: A master device must provide a hold time of at least 300ns for the SDA signal (referred to VIL of the SCL signal) to bridge
the undefined region of SCL’s falling edge.
Note 6: ISINK ≤6mA. Cb= total capacitance of one bus line in pF. tRand tFmeasured between 0.8V and 2.1V.
Note 7: Input filters on the SDA, SCL, and AD0 inputs suppress noise spikes less than 50ns.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
4 _______________________________________________________________________________________
GPO OUTPUT LOW VOLTAGE
vs. SINK CURRENT
MAX7347 toc01
ISINK (mA)
VOL (mV)
2015105
50
100
150
200
250
300
0
025
V+ = 2.4V
TA = +125°C
TA = +25°C
TA = -40°C
GPO OUTPUT LOW VOLTAGE
vs. SINK CURRENT
MAX7347 toc02
ISINK (mA)
VOL (mV)
2015105
50
100
150
200
250
300
0
025
V+ = 3V
TA = +125°C
TA = +25°C
TA = -40°C
GPO OUTPUT LOW VOLTAGE
vs. SINK CURRENT
MAX7347 toc03
ISINK (mA)
VOL (V)
2015105
50
100
150
200
250
300
0
025
V+ = 3.6V
TA = +125°C
TA = +25°C
TA = -40°C
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX7347 toc04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (μA)
3.43.22.6 2.8 3.0
45
50
55
60
65
70
75
80
85
90
40
2.4 3.6
TA = +125°C
TA = +25°C
TA = -40°C
KEY-SWITCH SOURCE CURRENT
vs. SUPPLY VOLTAGE
MAX7347 toc05
SUPPLY VOLTAGE (V)
KEY-SWITCH SOURCE CURRENT (μA)
3.43.22.6 2.8 3.0
25
26
27
28
29
30
24
2.4 3.6
TA = +125°C
COL0 = GND
TA = +25°C
TA = -40°C
SOUNDER FREQUENCY
vs. SUPPLY VOLTAGE
MAX7347 toc06
SUPPLY VOLTAGE (V)
SOUNDER FREQUENCY (Hz)
3.32.7 3.0
876
878
880
882
884
886
874
2.4 3.6
SOUNDER FREQUENCY
CONFIGURED FOR 880Hz
TA = +125°C
TA = +25°C
TA = -40°C
SOUNDER OUTPUT
MAX7347 toc07
3V
0V
VSOUNDER
1V/div
200μs/div
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX7347 toc08
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
3.32.7 3.0
61
62
63
64
65
60
2.4 3.6
OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX7347 toc09
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
11010 60
61
62
63
64
65
60
-40
Typical Operating Characteristics
(V+ = 3.3V, TA= +25°C, unless otherwise noted. Supply range for V+ is 2.4V to 3.6V. Temperature range is -40°C to +125°C.)
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
_______________________________________________________________________________________ 5
Detailed Description
The MAX7347/MAX7348/MAX7349 are microprocessor
peripherals that combine a low-noise key-switch inter-
face with a piezo sounder controller. Up to 64 key
switches can be monitored and debounced with optional
autorepeat, and the key events are presented in an
eight-deep FIFO. Key-switch functionality can be traded
to provide up to one (MAX7347), three (MAX7348), or six
(MAX7349) open-drain logic outputs. (Table 1).
The piezo sounder controller generates a variety of
audio tones. Tones are programmable for frequency
and duration, and may be intermittent, two tone, or con-
tinuous. The piezo sounder controller can be config-
ured to deliver an automatic, customizable sound on
every key press to provide a udible key-click feedback.
Interrupt requests can be configured to be issued on
every key-press event, or can be limited to a maximum
rate to prevent overloading the microprocessor with
Pin Description
PIN
MAX7347
(QSOP)
MAX7347
(TQFN) MAX7348 MAX7349
(QSOP)
MAX7349
(TQFN)
NAME FUNCTION
1 15 1 2 23 ROW0 Row Input from Key Matrix. Leave open circuit if unused.
2 16 2 3 24 ROW1 Row Input from Key Matrix. Leave open circuit if unused.
3 1 3 4 1 ROW2 Row Input from Key Matrix. Leave open circuit if unused.
4 2 4 5 2 ROW3 Row Input from Key Matrix. Leave open circuit if unused.
5 3 7 8 5 ROW4 Row Input from Key Matrix. Leave open circuit if unused.
6 4 8 9 6 ROW5 Row Input from Key Matrix. Leave open circuit if unused.
7 5 9 10 7 ROW6 Row Input from Key Matrix. Leave open circuit if unused.
8 6 10 11 8 ROW7 Row Input from Key Matrix. Leave open circuit if unused.
9 7 11 14 11 COL2/PORT2 Column Output to Key Matrix or GPO
10 8 12 15 12 COL1 Column Output to Key Matrix
11 9 13 16 13 COL0 Column Output to Key Matrix
12 10 15 18 15 GND Ground
13 11 17 20 17 SDA I2C-Compatible Serial Data I/O
14 12 18 21 18 SCL I2C-Compatible Serial Clock Input
15 13 19 22 19 INT Active-Low Interrupt Output. Output is open drain.
16 14 20 23 20 V+ Positive Supply Voltage. Bypass V+ to GND with a
0.047µF or higher ceramic capacitor.
— — 5 6 3 COL3/PORT3 Column Output to Key Matrix or GPO
— — 6 7 4 COL4/PORT4 Column Output to Key Matrix or GPO
— — 14 17 14 SOUNDER
S ound er D r i ver Outp ut. Typ i cal l y connect a p i ezo- cer am i c
sound er or other tr ansd ucer fr om thi s outp ut to g r ound .
O utp ut i s p ush- p ul l .
——161916 AD0
Address Input 0. Sets device slave address. Connect to
GND, V+, SDA, or SCL to give four logic combinations.
See Table 3.
— — — 1 22 COL7/PORT7 Column Output to Key Matrix or GPO
— — — 12 9 COL6/PORT6 Column Output to Key Matrix or GPO
— — — 13 10 COL5/PORT5 Column Output to Key Matrix or GPO
— — — 24 21 ALERT Alert Input. Connect to GND or V+ if unused.
—EP— —EP EP
E xp osed P ad d l e. Inter nal l y connected to GN D . C onnect to
a l ar g e g r ound p l ane to m axi m i ze ther m al p er for m ance.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
6 _______________________________________________________________________________________
too many interrupts. The key-switch status can be
checked at any time by reading the key-switch FIFO. A
1-byte read access returns both the first key-press
event in the FIFO (if there is one) and the FIFO status,
so it is easy to operate the MAX7347/MAX7348/
MAX7349 by polling. If the INT pin is not required, it
can be configured as an open-drain general-purpose
output (GPO) capable of driving an LED.
The MAX7349 monitors up to 64 keys. The MAX7348
monitors up to 40 keys. The MAX7347 monitors up to
24 keys (Table 1).
If the application requires fewer keys to be scanned, up
to six of the key-switch outputs can be configured as
open-drain GPOs capable of driving LEDs. For each
key-switch output used as a GPO, the number of key
switches that can be scanned is reduced by eight.
An alert logic input (MAX7349 only) can be configured
to deliver an automatic, customizable sound and/or an
interrupt on every falling edge of the logic input. The
logic state of the alert input can be read at any time.
Tone Generator
The piezo sounder controller generates a square wave
with the frequency of a musical tone under processor con-
trol. The selection of tones covers the 5th musical octave
(523.25Hz to 987.77Hz), plus seven other notes up to
2637Hz. The sounder output is also programmable to be
either high or low for the entire sound duration to operate
an electronic sounder, relay, or lamp instead of a piezo
transducer. The sound duration is programmable from
15.625ms in seven binary steps up to a maximum of 1s.
The piezo sounder controller interface uses a single 1-
byte access to its own separate slave address.
Commands are double-buffered to allow two commands
(2 bytes) to be stored and executed in succession. The
sounder controller performs the transition between
queued sound commands without click artifacts. The
controller can also autoloop between the two most
recent commands. Autolooping allows a wide range of
intermittent and two-tone sounds to be initiated, and
then run automatically without further intervention.
Key-Scan Controller
Key inputs are scanned statically, not dynamically, to
ensure low-EMI operation. As inputs only toggle in
response to switch changes, the key matrix can be
routed closer to sensitive circuit nodes.
The key controller debounces and maintains a FIFO of
key-press events (including autorepeated key presses,
if autorepeat is enabled). Figure 1 shows keys order.
Serial Interface
Figure 2 shows the 2-wire serial interface timing details.
Serial Addressing
The MAX7347/MAX7348/MAX7349 operate as slaves
that send and receive data through an I2C-compatible
2-wire interface. The interface uses a serial data line
(SDA) and a serial clock line (SCL) to achieve bidirec-
tional communication between master(s) and slave(s).
A master (typically a microcontroller) initiates all data
transfers to and from the MAX7347/MAX7348/MAX7349
and generates the SCL clock that synchronizes the
data transfer.
The MAX7347/MAX7348/MAX7349s’ SDA line operates
as both an input and an open-drain output. A pullup
resistor, typically 4.7kΩ, is required on SDA. The
MAX7347/MAX7348/MAX7349s’ SCL line operates only
as an input. A pullup resistor, typically 4.7kΩ, is required
on SCL if there are multiple masters on the 2-wire inter-
face, or if the master in a single-master system has an
open-drain SCL output.
Each transmission consists of a START condition
(Figure 3) sent by a master, followed by the MAX7347/
MAX7348/MAX7349 7-bit slave address plus R/Wbit, a
register address byte, 1 or more data bytes, and finally
a STOP condition.
Start and Stop Conditions
Both SCL and SDA remain high when the interface is
not busy. A master signals the beginning of a transmis-
sion with a START (S) condition by transitioning SDA
from high to low while SCL is high. When the master
has finished communicating with the slave, it issues a
PART PACKAGE-
PINS
MAXIMUM
KEY
SWITCHES
INT
OUTPUT
KEY-
SCAN
SLAVE
IDs
SOUNDER
SLAVE IDs
SOUNDER
OUTPUT GPOs ALERT
INPUT
MAX7349 24 64 Yes 4 4 Yes 6 + 1 (INT) Yes
MAX7348 20 40 Yes 4 4 Yes 3 + 1 (INT)—
MAX7347 16 24 Yes 1 fixed — — 1 + 1 (INT)—
Table 1. Product Features Table
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
_______________________________________________________________________________________ 7
STOP (P) condition by transitioning SDA from low to
high while SCL is high. The bus is then free for another
transmission.
Bit Transfer
One data bit is transferred during each clock pulse
(Figure 4). The data on SDA must remain stable while
SCL is high.
Acknowledge
The acknowledge bit is a clocked 9th bit (Figure 5),
which the recipient uses to handshake receipt of each
byte of data. Thus, each byte transferred effectively
requires 9 bits. The master generates the 9th clock
pulse, and the recipient pulls down SDA during the
acknowledge clock pulse, so the SDA line is stable low
during the high period of the clock pulse. When the
master is transmitting to the MAX7347/MAX7348/
MAX7349, the MAX7347/MAX7348/MAX7349 generate
the acknowledge bit because the MAX7347/MAX7348/
MAX7349 are the recipients. When the MAX7347/
MAX7348/MAX7349 are transmitting to the master, the
master generates the acknowledge bit because the
master is the recipient.
KEY
0
KEY
8
KEY
16
KEY
24
KEY
32
KEY
40
KEY
48
KEY
56
KEY
1
KEY
9
KEY
17
KEY
25
KEY
33
KEY
41
KEY
49
KEY
57
KEY
2
KEY
10
KEY
18
KEY
26
KEY
34
KEY
42
KEY
50
KEY
58
KEY
3
KEY
11
KEY
19
KEY
27
KEY
35
KEY
43
KEY
51
KEY
59
KEY
4
KEY
12
KEY
20
KEY
28
KEY
36
KEY
44
KEY
52
KEY
60
KEY
5
KEY
13
KEY
21
KEY
29
KEY
37
KEY
45
KEY
53
KEY
61
KEY
6
KEY
14
KEY
22
KEY
30
KEY
38
KEY
46
KEY
54
KEY
62
KEY
7
KEY
15
KEY
23
KEY
31
KEY
39
KEY
47
KEY
55
KEY
63
ROW0
ROW1
ROW2
ROW3
ROW4
ROW5
ROW6
ROW7
COL0
COL1
COL2/PORT2
COL3/PORT3*
COL4/PORT4*
COL5/PORT5**
COL6/PORT6**
COL7/PORT7**
*MAX7348 AND
MAX7349 ONLY.
**MAX7349 ONLY.
Figure 1. Keys Order
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
8 _______________________________________________________________________________________
SDA
SCL
tHD, STA
tLOW
tHIGH
tRtF
tSU, DAT tSU, STA
tSU, STO
tBUF
tHD, STA
tHD, DAT
START
CONDITION
STOP
CONDITION
START
CONDITION
REPEATED
START CONDITION
Figure 2. 2-Wire Serial Interface Timing Details
SDA
SCL
START
CONDITION
STOP
CONDITION
S P
Figure 3. Start and Stop Conditions
SDA
SCL
DATA LINE STABLE;
DATA VALID
CHANGE OF DATA
ALLOWED
Figure 4. Bit Transfer
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
_______________________________________________________________________________________ 9
Slave Addresses
The MAX7347/MAX7348/MAX7349 have two 7-bit long
slave addresses (Figure 6). The bit following a 7-bit
slave address is the R/Wbit, which is low for a write
command and high for a read command.
The first 4 bits (MSBs) of the MAX7347/MAX7348/
MAX7349 slave addresses are always 0111. Slave
address bits A3, A2, and A1 correspond, by the matrix
in Table 3, to the states of the device address input
AD0, and A0 corresponds to the R/Wbit. MAX7347/
MAX7348/MAX7349 use two slave addresses, one for
the main key-scan controller, and one for the sounder
controller. The AD0 input can be connected to any of
four signals: GND, V+, SDA, or SCL, giving four possible
slave address pairs, allowing up to four MAX7348/
MAX7349 devices to share the bus. Only one MAX7347
can share the bus. The MAX7347 AD0 input is internally
connected to GND.
The MAX7347/MAX7348/MAX7349 monitor the bus
continuously, waiting for a START condition followed by
its slave address. When MAX7347/MAX7348/MAX7349
recognize their slave address, they acknowledge and
are then ready for continued communication.
PIN COL0 COL1 COL2/PORT2 COL3/PORT3 COL4/PORT4 COL5/PORT5 COL6/PORT6 COL7/PORT7
ROW0 KEY 0 KEY 8 KEY 16 KEY 24 KEY 32 KEY 40 KEY 48 KEY 56
ROW1 KEY 1 KEY 9 KEY 17 KEY 25 KEY 33 KEY 41 KEY 49 KEY 57
ROW2 KEY 2 KEY 10 KEY 18 KEY 26 KEY 34 KEY 42 KEY 50 KEY 58
ROW3 KEY 3 KEY 11 KEY 19 KEY 27 KEY 35 KEY 43 KEY 51 KEY 59
ROW4 KEY 4 KEY 12 KEY 20 KEY 28 KEY 36 KEY 44 KEY 52 KEY 60
ROW5 KEY 5 KEY 13 KEY 21 KEY 29 KEY 37 KEY 45 KEY 53 KEY 61
ROW6 KEY 6 KEY 14 KEY 22 KEY 30 KEY 38 KEY 46 KEY 54 KEY 62
ROW7 KEY 7 KEY 15 KEY 23 KEY 31 KEY 39 KEY 47 KEY 55 KEY 63
Table 2. Key-Switch Mapping
DEVICE ADDRESS
PIN AD0 A7 A6 A5 A4 A3 A2 A1 A0 R/WFUNCTION
0 Key-scan controller write
01 Key-scan controller read
0 Sounder controller write
GND 011100
11 Sounder controller read
0 Key-scan controller write
01 Key-scan controller read
0 Sounder controller write
V+ 011101
11 Sounder controller read
0 Key-scan controller write
01 Key-scan controller read
0 Sounder controller write
SDA 011110
11 Sounder controller read
0 Key-scan controller write
01 Key-scan controller read
0 Sounder controller write
SCL 011111
11 Sounder controller read
Table 3. 2-Wire Interface Address Map
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
10 ______________________________________________________________________________________
Bus Timeout
The MAX7347/MAX7348/MAX7349 feature a 20ms mini-
mum bus timeout on the 2-wire serial interface, largely to
prevent the MAX7347/MAX7348/MAX7349 from holding
the SDA I/O low during a read transaction if the SCL
hangs for any reason before a serial transaction has
been completed. Bus timeout operates by causing the
MAX7347/MAX7348/MAX7349 to internally terminate a
serial transaction, either read or write, if the time between
adjacent edges on SCL exceeds 20ms. After a bus time-
out, the MAX7347/MAX7348/MAX7349 wait for a valid
START condition before responding to a consecutive
transmission. The bus timeout feature requires the serial
interface to operate above 50Hz bus speed. This feature
can be enabled or disabled under user control by writing
to the configuration register (Table 12).
Message Format for Writing the
Key-Scan Controller
A write to the MAX7347/MAX7348/MAX7349s’ key-scan
controller comprises the transmission of the
MAX7347/MAX7348/MAX7349s’ key-scan slave address
with the R/Wbit set to zero, followed by at least 1 byte of
information. The first byte of information is the command
byte. The command byte determines which register of the
MAX7347/MAX7348/MAX7349 is to be written by the next
byte, if received. If a STOP condition is detected after the
command byte is received, then the MAX7347/MAX7348
/MAX7349 take no further action (Figure 7) beyond stor-
ing the command byte.
Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register
of the MAX7347/MAX7348/MAX7349 selected by the
command byte (Figure 8).
If multiple data bytes are transmitted before a STOP
condition is detected, these bytes are generally stored
in subsequent MAX7347/MAX7348/MAX7349 internal
registers (Table 7) because the command byte address
generally autoincrements (Table 4).
Message Format for Reading the
Key-Scan Controller
The MAX7347/MAX7348/MAX7349 are read using the
MAX7347/MAX7348/MAX7349s’ internally stored com-
mand byte as an address pointer, the same way the
stored command byte is used as an address pointer for
a write. The pointer generally autoincrements after each
data byte is read using the same rules as for a write
(Table 4). Thus, a read is initiated by first configuring
the MAX7347/MAX7348/MAX7349s’ command byte by
performing a write (Figure 7). The master can now read
n consecutive bytes from the MAX7347/MAX7348/
MAX7349, with the first data byte being read from the
register addressed by the initialized command byte.
When performing read-after-write verification, remem-
ber to reset the command byte’s address because the
stored command byte address is generally autoincre-
mented after the write (Figure 9, Table 4).
SDA
SCL
01 1A3A2A11
MSB LSB
ACKR/W
Figure 6. Slave Address
SCL
SDA
BY
TRANSMITTER
CLOCK PULSE FOR
ACKNOWLEDGE
START
CONDITION
SDA
BY
RECEIVER
1 2 8 9
S
Figure 5. Acknowledge
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 11
Message Format for Writing the Sounder
Controller
A write to the MAX7347/MAX7348/MAX7349s’ sounder
controller comprises the transmission of the
MAX7347/MAX7348/MAX7349s’ sounder slave address
with the R/Wbit set to zero, followed by at least 1 com-
mand byte of information. The sounder controller ana-
lyzes each incoming data byte, and depending on the
state of the sounder controller’s 2-deep FIFO and the
contents of the command byte, the command byte is
added to the FIFO or it overwrites the last FIFO data
item (Table 16).
Message Format for Reading the Sounder
Controller
A read from the MAX7347/MAX7348/MAX7349s’ sounder
controller comprises the transmission of the
MAX7347/MAX7348/MAX7349s’ sounder slave address
with the R/Wbit set to 1. The master can now read n con-
secutive bytes from the MAX7347/MAX7348/MAX7349,
each byte being a snapshot of the FIFO status of the
sounder controller (Table 16). If the master wishes to poll
the sounder controller until there is room for another com-
mand to be sent, the master can read bytes continuously
from the sounder controller until the information is satis-
factory and then issue a STOP condition.
Operation with Multiple Masters
If the MAX7347/MAX7348/MAX7349 are operated on a 2-
wire interface with multiple masters, a master reading the
MAX7347/MAX7348/MAX7349 should use a repeated
start between the write that sets the MAX7347/MAX7348/
MAX7349s’ address pointer, and the read(s) that takes
the data from the location(s). This is because it is possi-
ble for master 2 to take over the bus after master 1 has
set up the MAX7347/MAX7348/MAX7349s’ address
pointer but before master 1 has read the data. If master 2
subsequently resets the MAX7347/MAX7348/MAX7349s’
address pointer, then master 1’s read may be from an
unexpected location.
REGISTER
FUNCTION
ADDRESS
CODE (hex)
AUTOINCREMENT
ADDRESS (hex)
Keys FIFO 0x00 0x00
Debounce 0x01 0x02
Autorepeat 0x02 0x03
Interrupt 0x03 0x04
Configuration 0x04 0x05
Port 0x05 0x06
Key Sound 0x06 0x07
Alert Sound 0x07 0x00
Table 4. Key-Scan Command Address
Autoincrement Rules
SAAP0SLAVE ADDRESS COMMAND BYTE
D7 D6 D5 D4 D3 D2 D1 D0
COMMAND BYTE IS STORED ON RECEIPT OF
ACKNOWLEDGE CONDITION
ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349
ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349
R/W
Figure 7. Command Byte Received
SAAAP0SLAVE ADDRESS COMMAND BYTE DATA BYTE
1 BYTE
AUTOINCREMENT
COMMAND BYTE ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 D1 D0D3 D2D5 D4D7 D6
ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349 ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349
ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349
R/W
Figure 8. Command and Single Data Byte Received
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
12 ______________________________________________________________________________________
REGISTER DATA
REGISTER
FUNCTION POWER-UP CONDITION ADDRESS
CODE (hex) D7 D6 D5 D4 D3 D2 D1 D0
Keys FIFO Empty 0x00 00000000
Debounce Ports 2–7 are enabled; debounce time is 39ms 0x01 11111111
Autorepeat Autorepeat is disabled 0x02 00000000
Interrupt INT is a port, not an interrupt output 0x03 00000000
Configuration
Shutdown mode: key sound is disabled; alert sound is
disabled; alert INT is disabled; timeout enabled; no
sound output
0x04 00000001
Ports Ports 2–7 and INT are logic-high (high impedance) 0x05 1111111X
Key Sound Key-sound default is 31.25ms of 987.77Hz 0x06 01010001
Alert Sound Key-sound default is 250ms of 2093Hz 0x07 10111011
Table 5. Key-Scan Power-Up Configuration
REGISTER DATA
POWER-UP CONDITION D7 D6 D5 D4 D3 D2 D1 D0
Sounder output is a general-purpose output, logic 0; queue is empty 0 0 0 0 0 0 0 0
Table 6. Sounder Power-Up Configuration
SAAAP0SLAVE ADDRESS COMMAND BYTE DATA BYTE
N BYTES
AUTOINCREMENT
COMMAND BYTE ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 D1 D0D3 D2D5 D4D7 D6
ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349 ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349
ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349
R/W
Figure 9. N Data Bytes Received
X
= Don’t care.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 13
Command Address Autoincrementing
Address autoincrementing allows the MAX7347/
MAX7348/MAX7349 to be configured with fewer trans-
missions by minimizing the number of times the com-
mand address needs to be sent. The command
address stored in the MAX7347/MAX7348/MAX7349
generally increments after each data byte is written or
read (Table 4). Autoincrementing applies only to the
key-scan command addresses and not to the sounder
command addresses.
Registers Description
Initial Power-Up
On power-up, all control registers are reset and the
MAX7347/MAX7348/MAX7349 enter shutdown mode
(Tables 5, 6). Table 7 shows the register address map
for the key-scan section.
COMMAND ADDRESS
REGISTER
FUNCTION D15 D14 D13 D12 D11 D10 D9 D8
ADDRESS
CODE
(hex)
Keys FIFO 000000000x00
Debounce 000000010x01
Autorepeat 000000100x02
Interrupt 000000110x03
Configuration 000001000x04
Ports 000001010x05
Key Sound 000001100x06
Alert Sound 000001110x07
Table 7. Key-Scan Register Address Map
REGISTER DATA
REGISTER
ADDRESS
CODE
(hex) D7 D6 D5 D4 D3 D2 D1 D0
KEYS FIFO REGISTER* 0X00 OVERFLOW
FLAG
MORE
FLAG
KEY SWITCH THAT HAS BEEN
DEBOUNCED
FIFO has not overflowed 0x00 0 X X X X X X X
FIFO overflowed; FIFO contains the first eight
key events 0x00 1 X X X X X X X
This key is the last FIFO item (key-switch data
not zero) 0x00 X 0 X X X X X X
Key 0 was EITHER the last FIFO item OR the
FIFO is empty and no key has been pressed 0x00 0 0 0 0 0 0 0 0
This key is not the last FIFO item 0x00 X 1 X X X X X X
Power-up default setting 0x00 0 0 0 0 0000
Table 8. Keys FIFO Register Format
*
Reading the key-scan FIFO clears the INT. INT is only reasserted by a key event after the FIFO has been emptied by read(s).
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
14 ______________________________________________________________________________________
Key-Scan Registers
Eight key-scan registers are described in the following
sections.
Keys FIFO Register
The keys FIFO register contains the information pertain-
ing to the status of the keys FIFO, as well as the key-
press events that have been debounced (Table 8). Bits
D0 to D5 denote which of the 64 keys have been
debounced and the keys are numbered as in Table 2
and Figure 1. D6 indicates whether the present
debounced key is the last one in the FIFO, with 1
denoting that there are more keys after the present one,
and 0 denoting that the present debounced key is the
last one stored in the FIFO. D7 is the overflow flag,
which denotes whether the keys FIFO has overflowed.
Reading the key-scan FIFO clears the interrupt INT. INT
is only reasserted after the FIFO has been emptied by
performing enough read operations.
Debounce Register
The debounce register sets the time for each debounce
cycle, as well as setting whether the GPO ports are
enabled or disabled. Bits D0 through D4 set the
debounce time in increments of 1ms starting at 9ms
and ending at 40ms (Table 9). Bits D5 through D7 set
which one of the GPO ports is to be enabled. Note that
not any port can be enabled at a particular time. The
GPO ports can be enabled only in the combinations
shown in Table 9, from all disabled to all enabled.
Autorepeat Register
The autorepeat register sets the autorepeat frequency
(repeat rate) and its delay. The autorepeat function allows
a key to be consecutively asserted when the key itself is
pressed down without being released. The autorepeat
delay specifies the delay between the first press and the
beginning of the autorepeating, provided that the key has
not been released. The autorepeat frequency specifies
how fast the continuously pressed-down key to be assert-
ed once autorepeating has started is. Bits D0 through D3
specify the autorepeat delay in terms of debounce cycles
REGISTER ADDRESS CODE
(hex) REGISTER DATA
D7 D6 D5 D4 D3 D2 D1 D0
DEBOUNCE REGISTER 0x01 PORTS ENABLE DEBOUNCE TIME
Debounce time is 9ms 0x01 X X X 0000 0
Debounce time is 10ms 0x01 X X X 0000 1
Debounce time is 11ms 0x01 X X X 0001 0
Debounce time is 12ms 0x01 X X X 0001 1
All the way through to 0x01 X X X ———— —
Debounce time is 37ms 0x01 X X X 1110 0
Debounce time is 38ms 0x01 X X X 1110 1
Debounce time is 39ms 0x01 X X X 1111 0
Debounce time is 40ms 0x01 X X X 1111 1
GPO ports disabled (full key-scan functionality) 0x01 0 0 0 XXXX X
GPO port 7 enabled 0x01 0 0 1 XXXX X
GPO ports 7 and 6 enabled 0x01 0 1 0 XXXX X
GPO ports 7, 6, and 5 enabled 0x01 0 1 1 XXXX X
GPO ports 7, 6, 5, and 4 enabled 0x01 1 0 0 XXXX X
GPO ports 7, 6, 5, 4, and 3 enabled 0x01 1 0 1 XXXX X
GPO ports 7, 6, 5, 4, 3, and 2 enabled 0x01 1 1 XXXXX X
Power-up default setting 0x01 1 111111 1
Table 9. Debounce Register Format
MAX7347/MAX7348/MAX7349
ranging from 8 debounce cycles to 128 debounce cycles
(Table 10). Bits D4 through D6 specify the autorepeat
rate or frequency ranging from 4 to 32 debounce cycles.
Bit D7 specifies whether the auto-repeat function is
enabled with 0 denoting autorepeat disabled and 1
denoting autorepeat enabled.
Interrupt Register
The interrupt register contains information related to the
settings of the interrupt request function, as well as the
status of the INT output, which can also be configured
as a GPO. Bits D0 through D4 set the key-scan interrupt
frequency. By setting bits D0 through D4 to an appropri-
ate value, the interrupt can be asserted at the end of the
selected number of debounce cycles (Table 11). This
number ranges from 1 to 31 debounce cycles. If bits D0
through D4 are set to 00000, the INT output is config-
ured as a GPO that is controlled by bit D6 in the ports
register and the INT output is not asserted. However, the
INT status bits D5, D6, and D7 are still set and cleared in
the normal way at the end of each debounce cycle as if
bits D0 through D4 were set to 00001.
Bits D5 and D6 denote whether an interrupt was set
due to a key-scan event (bit D5) or to an alert event (bit
D6). Bit D7 represents whether an interrupt request has
been asserted with 0 denoting no INT asserted and 1
denoting that INT has been asserted.
The interrupt register is a read-only register and writes
to it are ignored. Reading the interrupt register does
clear an alert event INT, but does not clear a key-scan
event INT. An interrupt request caused by a key-scan
event(s) is cleared when the FIFO is emptied.
Configuration Register
The configuration register reflects the sounder status,
controls the I2C bus timeout feature, enables the alert
input interrupt feature, enables the sounder to respond
to both alert input and key debounce events, and con-
trols the shutdown of the device (Table 12).
Ports Register
The ports register sets the values of ports 2 through 7 and
the INT port when configured as GPOs. The settings in
this register are ignored for ports not configured as
GPOs, and a read from this register returns the values
stored in the register and not the actual port conditions
(Table 13). The ports register also serves to read the alert
input and this is done through bit D0 with a 0 denoting a
low on the alert input and a 1 denoting a high.
Key-Sound Register
The key-sound register specifies the duration and fre-
quency of the sound to be executed by the sounder con-
troller when a key or a set of keys are debounced if the
sounder output has been enabled to be set by a key
debounce event in the configuration register. When this
happens, the information of bits D7 through D1 is passed
on to the sounder register and the appropriate sound is
executed (Tables 14, 16). Least significant bit D0 is
ignored and always set to 1 when transferred to the
sounder register. See Table 16 for the format of setting
the frequency and duration of the sound to be executed.
If a key-sound register command is sent as 000xxxx
(continuous), then the command is stored as 111xxxx
(1000ms) in the sounder register.
Alert Sound Register
The alert sound register specifies the duration and fre-
quency of the sound to be executed by the sounder con-
troller at the falling edge of the alert input if the sounder
output has been enabled to be set by the alert input in
the configuration register. If this is the case, the informa-
tion of bits D7 through D1 is passed on to the sounder
register and the appropriate sound is executed (Tables
15, 16). Least significant bit D0 is always set to 1 and
this value is ignored when transferred to the sounder
register. See Table 16 for the proper format of setting the
frequency and duration of the sound to be executed.
Note that if an alert sound register command is sent as
000xxxx (continuous), then the command is actually
stored as 111xxxx (1000ms) in the sounder register.
Sounder Register
The sounder register stores the frequencies and duration
of the sounds to be executed by the sounder, as well as
the state of its two-deep FIFO (Table 16). D0 denotes
whether another command is lined in the queue at any
given moment. A 0 in D0 denotes that the queue is empty
while a 1 denotes that there is another command. By writ-
ing 0 to D0, the present command is executed and the
queue is cleared. When sending a command that has a
D0 set to 1, the queue is checked and, if empty, the sent
command is added to it while, if full, the sent command
replaces the queued command.
Bits D0 and D1, when taken in conjunction, set the level
of the sounder output when configured as a GPO and
also control the autoloop function provided that the rest of
the bits (D7 through D2) are set to 0. When the sounder is
configured as a GPO, the levels of the output are set by
D1, a 0 denoting a low and a 1 denoting a high. When D0
is set to 1 and the rest of the bits are set to 0, D1 controls
the autoloop function as defined in Table 16.
Bits D7 through D1 control the frequency and duration of
the sounds to be executed by the sounder. These sounds
include the musical notes of the 5th octave plus some
notes from the 6th and 7th octaves as well. See Table 16.
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 15
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
16 ______________________________________________________________________________________
REGISTER DATA
REGISTER
ADDRESS
CODE
(hex) D7 D6 D5 D4 D3 D2 D1 D0
AUTOREPEAT REGISTER 0x02 ENABLE AUTOREPEAT
RATE AUTOREPEAT DELAY
Autorepeat is disabled 0x02 0 X X X X X X X
Autorepeat is enabled 0x02 1 AUTOREPEAT
RATE AUTOREPEAT DELAY
Key-switch autorepeat delay is 8 debounce cycles 0x02 1 X X X 0000
Key-switch autorepeat delay is 16 debounce cycles 0x02 1 X X X 0001
Key-switch autorepeat delay is 24 debounce cycles 0x02 1 X X X 0010
Key-switch autorepeat delay is 32 debounce cycles 0x02 1 X X X 0011
Key-switch autorepeat delay is 40 debounce cycles 0x02 1 X X X 0100
Key-switch autorepeat delay is 48 debounce cycles 0x02 1 X X X 0101
Key-switch autorepeat delay is 56 debounce cycles 0x02 1 X X X 0110
Key-switch autorepeat delay is 64 debounce cycles 0x02 1 X X X 0111
Key-switch autorepeat delay is 72 debounce cycles 0x02 1 X X X 1000
Key-switch autorepeat delay is 80 debounce cycles 0x02 1 X X X 1001
Key-switch autorepeat delay is 88 debounce cycles 0x02 1 X X X 1010
Key-switch autorepeat delay is 96 debounce cycles 0x02 1 X X X 1011
Key-switch autorepeat delay is 104 debounce cycles 0x02 1 X X X 1100
Key-switch autorepeat delay is 112 debounce cycles 0x02 1 X X X 1101
Key-switch autorepeat delay is 120 debounce cycles 0x02 1 X X X 1110
Key-switch autorepeat delay is 128 debounce cycles 0x02 1 X X X 1111
Key-switch autorepeat frequency is 4 debounce cycles 0x02 1 0 0 0 XXXX
Key-switch autorepeat frequency is 8 debounce cycles 0x02 1 0 0 1 XXXX
Key-switch autorepeat frequency is 12 debounce cycles 0x02 1 0 1 0 XXXX
Key-switch autorepeat frequency is 16 debounce cycles 0x02 1 0 1 1 XXXX
Key-switch autorepeat frequency is 20 debounce cycles 0x02 1 1 0 0 XXXX
Key-switch autorepeat frequency is 24 debounce cycles 0x02 1 1 0 1 XXXX
Key-switch autorepeat frequency is 28 debounce cycles 0x02 1 1 1 0 XXXX
Key switch autorepeat frequency is 32 debounce cycles 0x02 1 1 1 1 XXXX
Power-up default setting 0x02 0 0000000
Table 10. Autorepeat Register Format
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 17
REGISTER DATA
REGISTER ADDRESS
CODE (hex) D7 D6 D5 D4 D3 D2 D1 D0
INTERRUPT REGISTER 0x03 INT
STATUS*
ALERT
EVENT*
KEY-
SCAN
EVENT*
KEY-SCAN INTERRUPT
FREQUENCY
Current INT is due to key-scan event(s) 0x03 1 0 1 X X X X X
Current INT is due to alert event 0x03 1 1 0 X X X X X
Current INT is due to both key-scan event(s)
and alert event 0x03 1 1 1 X X X X X
INT has not been asserted 0x03 0 0 0 X X X X X
INT has been asserted 0x03 1 ALERT
EVENT
KEY-
SCAN
EVENT
XXXXX
INT output pin is NOT asserted; INT output
pin is used as a general-purpose output
called INT port under control of bit D6 in
ports register; INT status bits D5, D6, D7 are
still set and cleared in the normal way at the
end of every debounce cycle as if bits D4–D0
were set to 00001
0x03 X X X 0 0 0 0 0
Key-scan INT is asserted at the end of every
debounce cycle, if new key(s) is debounced 0x03 X X X 0 0 0 0 1
Key-scan INT is asserted at the end of every
2 debounce cycles, if new key(s) is
debounced
0x03 X X X 0 0 0 1 0
-— — — — — — — — —
Key-scan INT is asserted at the end of every
29 debounce cycles, if new key(s) is
debounced
0x03 X X X 1 1 1 0 1
Key-scan INT is asserted at the end of every
30 debounce cycles, if new key(s) is
debounced
0x03 X X X 1 1 1 1 0
Key-scan INT is asserted at the end of every
31 debounce cycles, if new key(s) is
debounced
0x03 X X X 1 1 1 1 1
Power-up default setting 0x03 00000000
Table 11. Interrupt Register Format
*
Read-only register bits; write data is ignored. Reading the interrupt register does clear an alert event INT, but does not clear a key-
scan event INT. INT caused by key-scan event(s) is cleared when FIFO is emptied.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
18 ______________________________________________________________________________________
REGISTER DATA
REGISTER ADDRESS
CODE (hex) D7 D6 D5 D4 D3 D2 D1 D0
CONFIGURATION REGISTER 0x04 SHUTDOWN
KEY
SOUND
ENABLE
ALERT
SOUND
ENABLE
ALERT
INT
ENABLE
ALERT
INT
EVENT
SOUNDER
STATUS
T I M EO U T
EN A B L E
Serial interface bus timeout enabled 0x04 X X X X X X X 0
Serial interface bus timeout disabled 0x04 X X X X X X X 1
No active sounder output 0x04 X X X X X 0 0 X
Active sounder output set by serial
interface 0x04 X X X X X 0 1 X
Active sounder output set by key
debounce event 0x04 X X X X X 1 0 X
Active sounder output set by an alert
event 0x04 X X X X X 1 1 X
Alert input interrupt (if enabled) is
asserted according to key-scan
interrupt rules
0x04 X X X X 0 X X X
Alert input interrupt (if enabled) is
asserted immediately 0x04 X X X X 1 X X X
Alert input does not cause an
interrupt 0x04 X X X 0 X X X X
Falling edge of alert input causes
interrupt 0x04 X X X 1 X X X X
Alert input does not cause an
automatic sound 0x04 X X 0 X X X X X
Falling edge of alert input causes the
8-bit contents of the alert sound
register 0x07 to be sent to the
sounder
0x04 X X 1 X X X X X
Debounce key(s) do not cause an
automatic sound 0x04 X 0 X X X X X X
Debounced key(s), including
autorepeated keys, cause the 8-bit
contents of the key-sound register
0x06 to be sent to the sounder
0x04 X 1 X X X X X X
Table 12. Configuration Register Format
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 19
REGISTER DATA
REGISTER ADDRESS
CODE (hex) D7 D6 D5 D4 D3 D2 D1 D0
CONFIGURATION REGISTER 0x04 SHUTDOWN
KEY
SOUND
ENABLE
ALERT
SOUND
ENABLE
ALERT
INT
ENABLE
ALERT
INT
EVENT
SOUNDER
STATUS
T IM EO U T
EN A B L E
Shutdown mode; key-scan and
sounder timing are disabled,
interrupts disabled, but alert input
can be read and port outputs (as
selected) can be changed
0x04 0 X X X X X X X
Operating mode; key scan is started,
and commands in sounder queue
are actioned
0x04 1 X X X X X X X
Power-up default setting 0x04 00000001
Table 12. Configuration Register Format (continued)
REGISTER DATA
REGISTER ADDRESS
CODE (hex)
READ
WRITE D7 D6 D5 D4 D3 D2 D1 D0
READ PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2 INT
PORT
ALERT
INPUT
PORTS REGISTER 0x05
WRITE PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2 INT
PORT X
Clear port 2 low 0x05 Write X X X X X 0 X X
Set port 2 high (high
impedance) 0x05 Write X X X X X 1 X X
Clear port 3 low 0x05 Write X X X X 0 X X X
Set port 3 high (high
impedance) 0x05 Write X X X X 1 X X X
Clear port 4 low 0x05 Write X X X 0 X X X X
Set port 4 high (high
impedance) 0x05 Write X X X 1 X X X X
Clear port 5 low 0x05 Write X X 0 X X X X X
Set port 5 high (high
impedance) 0x05 Write X X 1 X X X X X
Clear port 6 low 0x05 Write X 0 X X X X X X
Set port 6 high (high
impedance) 0x05 Write X 1 X X X X X X
Table 13. Ports Register Format
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
20 ______________________________________________________________________________________
REGISTER DATA
REGISTER ADDRESS
CODE (hex)
READ
WRITE D7 D6 D5 D4 D3 D2 D1 D0
READ PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2 INT
PORT
ALERT
INPUT
PORTS REGISTER 0x05
WRITE PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2 INT
PORT X
Clear port 7 low 0x05 Write 0 X X X X X X X
Set port 7 high (high
impedance) 0x05 Write 1 X X X X X X X
Clear INT port low;
this setting is ignored
unless the key-scan INT
functionality is disabled
by setting interrupt
register bits D4 to D0 to
00000
0x05 Write X X X X X X 0 X
Set INT port high (high
impedance); this setting
is ignored unless the
key-scan INT
functionality is disabled
by setting interrupt
register bits D4 to D0 to
00000
0x05 Write X X X X X X 1 X
Alert input level is low 0x05 Read X X X X X X X 0
Alert input level is high 0x05 Read X X X X X X X 1
Power-up default
setting 0x05 — 1111111X
Table 13. Ports Register Format (continued)
REGISTER DATA
REGISTER ADDRESS
CODE (hex) D7 D6 D5 D4 D3 D2 D1 D0
This-8 bit value is passed to sounder controller when key(s)
debounced, if enabled in the configuration register; these 7
bits define duration and frequency only; sounder command
bit D0 is ignored and fixed internally at 1; if a key sound is
sent as 000xxxxx (continuous), then the command is stored
as 111xxxxx (1000 ms)
0x06 7-bit value (see Table 16 for functionality) 1
Power-up default setting 0x06 01010001
Table 14. Key-Sound Register Format
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 21
REGISTER DATA
REGISTER ADDRESS
CODE (hex) D7 D6 D5 D4 D3 D2 D1 D0
This 8-bit value is passed to sounder controller on the falling
edge of the alert input; these 7 bits define duration and
frequency only; sounder command bit D0 is ignored and
fixed internally at 1; if an alert sound is sent as 000xxxxx
(continuous), then the command is stored as 111xxxxx
(1000 ms)
0x07 7-bit value (see Table 16 for functionality) 1
Power-up default setting 0x07 10111011
Table 15. Alert Sound Register Format
REGISTER DATA
REGISTER D7 D6 D5 D4 D3 D2 D1 D0
SOUNDER REGISTER
READ
WRITE
DURATION FREQUENCY LEVEL BUFFER
No commands are active; OR output is GPO logic 0 Read 0 0 0 0 0 0 0 0
This current command is active, none are queued (so another
command may be sent) Read DURATION FREQUENCY LEVEL 0
This current command is active, and another command is in
the queue Read DURATION FREQUENCY LEVEL 1
Perform this command, terminating and clearing any previous
active command, command queue, and autoloop; new
command is now active, and queue is now empty
Write X X X X X X X 0
Add command to queue if not full; command replaces queued
command if queue is full Write X X X X X X X 1
Configure sounder output as general-purpose output, logic 0
(clear queue; sounder output active low with continuous
duration, ie, until a buffer = 0 command)
Write 0 0 0 0 0 0 0 0
Configure sounder output as general-purpose output, logic 1
(clear queue; sounder output active high with continuous
duration, ie, until a buffer = 0 command)
Write 0 0 0 0 0 0 1 0
Autoloop using the current two commands; the active
command is command 1, and the inactive command is
command 2; if no command is active, the oldest command is
reactivated as command 1, and the other command is re-
activated as command 2
Write 0 0 0 0 0 0 0 1
Autoloop is halted at the end of command 2, and output idles
as defined by command 2 Write 0 0 0 0 0 0 1 1
Table 16. Sounder Register Format
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
22 ______________________________________________________________________________________
REGISTER DATA
REGISTER D7 D6 D5 D4 D3 D2 D1 D0
SOUNDER REGISTER
READ
WRITE
DURATION FREQUENCY LEVEL BUFFER
Sounder output active low for sound duration;
queue cleared — Write 0 0 0 0 0
Sounder output active high for sound duration;
queue cleared — Write 0 0 0 1 0
Sound frequency is 523.25Hz, idles low Note C5 Write 0 0 1 0
Sound frequency is 587.33Hz, idles low Note D5 Write 0 0 1 1
Sound frequency is 659.26, idles low Note E5 Write 0 1 0 0
Sound frequency is 698.46Hz, idles low Note F5 Write 0 1 0 1
Sound frequency is 783.99Hz, idles low Note G5 Write 0 1 1 0
Sound frequency is 880Hz, idles low Note A5 Write 0 1 1 1
Sound frequency is 987.77Hz, idles low Note B5 Write 1 0 0 0
Sound frequency is 1046.5Hz, idles low Note C6 Write 1 0 0 1
Sound frequency is 1318.5Hz, idles low Note E6 Write 1 0 1 0
Sound frequency is 1568Hz, idles low Note G6 Write 1 0 1 1
Sound frequency is 1760Hz, idles low Note A6 Write 1 1 0 0
Sound frequency is 2093Hz, idles low Note C7 Write 1 1 0 1
Sound frequency is 2349.3Hz, idles low Note D7 Write 1 1 1 0
Sound frequency is 2637Hz, idles low Note E7 Write
DURATION
111 1
BUFFER
Sound duration is continuous; if an alert sound or
a key sound is programmed as 000xxxxx
(continuous), then the command is treated as
111xxxxx (1000 ms)
Write 0 0 0
Sound duration is 15625ms* Write 0 0 1
Sound duration is 3125ms* Write 0 1 0
Sound duration is 625ms* Write 0 1 1
Sound duration is 125ms* Write 1 0 0
Sound duration is 250ms* Write 1 0 1
Sound duration is 500ms* Write 1 1 0
Sound duration is 1000ms* Write 1 1 1
FREQUENCY LEVEL BUFFER
Power-up default setting —000000 0 0
Table 16. Sounder Register Format (continued)
*
Sound duration will be slightly longer than these times because each sound always completes a full cycle before stopping.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 23
Sounder Operation
When an alert sound or key sound is happening, the user
cannot write to the sounder. The MAX7347/MAX7348/
MAX7349 do not acknowledge a write to the sounder I2C
address. However, a read from the sounder will work cor-
rectly. An alert sound or key sound event terminates a
current user-programmed event and clears the queue. If
an alert sound or key sound event is currently being
processed, then a new alert sound or key sound event
will be put into the queue, replacing an existing queued
alert sound or key sound event, if one exists. User access
to the sounder is restored when the last alert sound or key
sound event is completed. Note this means that the buffer
bit (D0) for an alert sound or key sound command is
effectively ignored.
Shutdown
The MAX7347/MAX7348/MAX7349 are put into shut-
down mode by clearing bit D7 in the configuration reg-
ister (Table 12). In shutdown, the key-scan controller
and sounder controller are both disabled, and the
MAX7347/MAX7348/MAX7349 draw minimal current.
No additional supply current is drawn if any keys are
pressed. All switch matrix current sources are turned
off, and row outputs ROW0 to ROW7 and column out-
puts COL0 to COL7 become high impedance.
The alert input status may still be read in shutdown,
and an alert event can still cause an interrupt request if
this feature is enabled (Table 12). This means that alert
can be used for µC wakeup while the system sleeps
drawing minimum current.
Outputs configured as GPOs (COL2/PORT2 to
COL2/PORT7 and INT) may still be controlled in shut-
down and their output states can be changed under
software control at any time.
The sounder output may not be changed in shutdown,
even if it is effectively being used as a logic output. Writes
to the sounder during shutdown are ignored, and the
sounder FIFO is cleared on entering shutdown. However,
the sounder retains its output logic state for the duration
of shutdown, and so can be set low or high as desired by
writing 0x00 or 0x02, respectively, to the sounder register
(Table 12) before entering shutdown.
The MAX7347/MAX7348/MAX7349 may be taken out of
shutdown mode and put into operating mode by setting
bit D7 in the configuration register (Table 12). The key-
scan and sounder controller FIFOs are cleared, and key
monitoring starts. Note that rewriting the configuration
register with bit D7 high when bit D7 was already high
does not clear the FIFOs; the FIFOs are only cleared
when the MAX7347/MAX7348/MAX7349 are actually
coming out of shutdown.
Applications Information
Ghost-Key Elimination
Ghost keys are a phenomenon inherent with key-switch
matrices. When three switches located at the corners of
a matrix rectangle are pressed simultaneously, the
switch that is located at the last corner of the rectangle
(the ghost key) also appears to be pressed. This occurs
because the potentials at the two sides of the ghost-key
switch are identical due to the other three connections—
the switch is electrically shorted by the combination of
the other three switches (Figure 10). Because the key
appears to be pressed electrically, it is impossible for
software to detect which of the four keys is the ghost key.
The MAX7347/MAX7348/MAX7349 employ a proprietary
scheme that detects any three-key combination that
generates a fourth ghost key, and does not report any of
these four keys as being pressed. This means that
although ghost keys are never reported, many combina-
tions of three keys are effectively ignored when pressed
at the same time. Applications requiring three key com-
binations (such as <Ctrl><Alt><Del>) must ensure that
the 3 keys are not wired in positions that define the ver-
tices of a rectangle (Figure 11).
Low-EMI Operation
The MAX7347/MAX7348/MAX7349 use two techniques
to minimize EMI radiating from the key-switch wiring.
First, the voltage across the switch matrix never
exceeds 0.65V, irrespective of supply voltage V+. This
reduces the voltage swing at any node when a switch
is pressed to 0.65V maximum. Second, the keys are not
dynamically scanned, which would cause the key-
switch wiring to continuously radiate interference.
Instead, the keys are monitored for current draw (only
occurs when pressed), and debounce circuitry only
operates when one or more keys are actually pressed.
Power-Supply Considerations
The MAX7347/MAX7348/MAX7349 operate with a 2.4V
to 3.6V power-supply voltage. Bypass the power supply
to GND with a 0.047µF or higher ceramic capacitor as
close to the device as possible.
Switch On-Resistance
The MAX7347/MAX7348/MAX7349 are designed to be
insensitive to resistance either in the key switches or
the switch routing to and from the appropriate COLx
and ROWx up to 1kΩ. These controllers are therefore
compatible with low-cost membrane and conductive
carbon switches.
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
24 ______________________________________________________________________________________
Audio Transducers
The sounder output is designed to drive a standard, low-
cost piezo transducer directly without further buffering.
Piezo transducers appear as a capacitive load of typical-
ly 10nF. If a resistive or inductive sounder is used, such
as a small loudspeaker, fit a coupling capacitor between
the sounder output and the transducer. For example, if a
32Ωspeaker is used, connect the positive side of a 22µF
electrolytic capacitor to the sounder output, the negative
side of the capacitor to one end of the speaker, and the
other end of the speaker to GND.
The sounder output can also drive a power amplifier for
higher sound levels. In this case, it is usually desirable
to include a lowpass filter before the speaker to convert
the square-wave tones to something closer to a sinu-
soid. The recommended cutoff frequency of this filter is
around 3kHz. An example circuit is shown in Figure 12,
which uses the uncommitted op amp of the MAX4366
bridge power amplifier to implement a third-order
Chebyshev lowpass filter.
REGULAR KEY-PRESS
EVENT
GHOST-KEY
EVENT
KEY-SWITCH MATRIX
Figure 10. Ghost-Key Phenomenon
KEY-SWITCH MATRIX KEY-SWITCH MATRIX
EXAMPLES OF VALID THREE-KEY COMBINATIONS
Figure 11. Valid Three-Key Combinations
Chip Information
PROCESS: BiCMOS
21.5kΩ32.4kΩ
22nF
SOUNDER
OUTPUT
SHUTDOWN
2.61kΩ
68nF
21.5kΩ
220pF
IN-
IN+
SHDN
BIAS
10kΩ
10kΩ
50kΩ
50kΩ
VCC
OUT-
OUT+
0.22μF
16Ω
MAX4366
Figure 12. Third-Order Chebyshev Lowpass Filter and Output Stage
MAX7347/MAX7348/MAX7349
MAX7348
ROW0
ROW1
ROW2
ROW3
ROW4
ROW5
ROW6
ROW7
COL0
COL1
COL2/PORT2
GND
V+
COL3/PORT3
COL4/PORT4
AD0
SCL
SDA
INT
SCL
SDA
INT
3.3V
GND
V+
3.3V3.3V
5V
SOUNDER
PIEZOELECTRIC
TRANSDUCER
KEY 0
KEY 1
KEY 2
KEY 3
KEY 4
KEY 5
KEY 6
KEY 7
KEY 8
KEY 9
KEY 10
KEY 11
KEY 12
KEY 13
KEY 14
KEY 15
KEY 16
KEY 17
KEY 18
KEY 19
KEY 20
KEY 21
KEY 22
KEY 23
Typical Application Circuit
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 25
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
26 ______________________________________________________________________________________
20
19
18
17
16
15
14
13
1
2
3
4
5
6
7
8
V+
SCL
SDAROW3
ROW2
ROW1
ROW0
TOP VIEW
AD0
GND
SOUNDER
COL0ROW5
ROW4
COL4/PORT4
COL3/PORT3
12
11
9
10
COL1
COL2/PORT2ROW7
ROW6
MAX7348
QSOP
INT
+
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
ALERT
V+
SCLROW2
ROW1
ROW0
COL7/PORT7
TOP VIEW
SDA
AD0
GND
SOUNDERROW4
COL4/PORT4
COL3/PORT3
ROW3
16
15
14
13
9
10
11
12
COL0
COL1
COL2/PORT2
COL5/PORT5COL6/PORT6
ROW7
ROW6
ROW5
QSOP
MAX7349
INT
+
Pin Configurations
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
ROW0 V+
SCL
SDA
GND
COL0
COL1
COL2/PORT2
TOP VIEW
MAX7347
QSOP
INTROW1
ROW2
ROW5
ROW3
ROW4
ROW6
ROW7
+
MAX7349
19
20
21
22
12 3456
18 17 16 15 14 13
23
24
12
11
10
9
8
7
INT
ALERT
V+
COL7/PORT7
ROW1
ROW2
ROW3
COL3/PORT3
COL4/PORT4
ROW4
ROW5
SCL
SDA
GND
SOUNDER
COL0
ROW0
COL1
COL5/PORT5
COL2/PORT2
COL6/PORT6
ROW6
ROW7
AD0
TOP VIEW
TQFN-EP
+EP*
*EP = EXPOSED PADDLE
15
16
14
13
6
5
7
ROW3
ROW5
8
ROW2
SDA
COL0
SCL
12
V+
4
12 11 9
ROW0
ROW1
COL1
COL2/PORT2
ROW7
ROW6
EP*
*EP = EXPOSED PADDLE
MAX7347
ROW4 GND
3
10
INT
TQFN-EP
TOP VIEW
+
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
______________________________________________________________________________________ 27
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
QSOP.EPS
F11
21-0055
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
28 ______________________________________________________________________________________
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
PACKAGE OUTLINE,
21-0139 2
1
E
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
MAX7347/MAX7348/MAX7349
2-Wire Interfaced Low-EMI Key Switch
and Sounder Controllers
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
29
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE,
21-0139
2
2
E
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
Revision History
Pages changed at Rev 5: 1, 2, 23, 29
