MDS 712 L 1Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
TOUCH SCREEN CONTROLLER
MK712
Description
The MK712 Touch Screen Controller IC provides all the
screen drive, A to D converter and control circuits to
easily interface to 4-wire analog resistive touch
screens.
The IC continually monitors the screen waiting for a
touch. In this mode, the supply current is typically
0.5µA. When the screen is touched, the IC performs
analog to digital conversions to determine the location
of the touch, stores the X and Y locations in the
registers, and issues an interrupt. This process is
repeated up to 197 times per second until no further
screen touches are detected, at which time the low
current mode is resumed.
Block Diagram
Features
•Packaged in 28-pin SSOP (150 mil) or 28-pin SOIC
(300 mil)
•Industrial (-30°C to +70°C) and commercial (0 to
+70°C) and automotive (-35°C to +85°C)
temperature ranges
•Available in Pb (lead) free
•Fully integrated, lowest power solution
•Low standby current of 0.5µA (typical) at 5.0 V
•Active current while converting less than 10 mA
•Resolves 350 dots/inch on 10.5” display
•Maximum speed of 197 points/second
•Ratio metric conversion may eliminate screen
calibration
•Automatically wakes up and goes back to standby
•3.3 V or 5 V supply
•12 bit A/D converter
•Simplifies the writing of software for touch screens
•Extended temperature range available
•Capacitors are the only external components
required
•Touch screen is directly driven - no external
transistors are required
•Programmable conversion rate
•A to D Converter is monotonic
•Parallel interface
•See the MK715 for a serial interface
TOUCH SCREEN CONTROLLER
MDS 712 L 2Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Pin Assignment
Pin Descriptions
18
7
17
8
16
9
15
XL
10
YH
11
YL
12
GND
13
GND
14
GND
D6
D7
CLKIN
WR A0
A2
RD A1
22
21
20
19
CS
VDD
5
6
VDD
XH D5
24
23
D4
3
4
TOUCH
VDD D3
26
25
D2
1
2
NC
INT D1
28
27
D0
Pin
Number
Pin
Name
Pin Type Pin Description
1 NC — No connect. Do not connect this pin to anything.
2 INT Output Interrupt. Goes high to signal an interrupt. Cleared on next read.
3 TOUCH Output Touch signal. Goes low when screen is touched. Goes high when not touched.
4 VDD Power Power Supply. Connect to +5 V or +3.3 V. (Connect all VDDs to same voltage)
5 VDD Power Power Supply. Connect to +3.3 V.
6 XH Touch Screen Pin Connect to X-high on touch screen. (Right side)
7 XL Touch Screen Pin Connect to X-low on touch screen. (Left side)
8 YH Touch Screen Pin Connect to Y-high on touch screen. (Top)
9 YL Touch Screen Pin Connect to Y-low on touch screen. (Bottom)
10 GND Power Connect to ground.
11 GND Power Connect to ground.
12 WR Input Write enable. Active low.
13 RD Input Read enable. Active low.
14 CS Input Chip select. Active low.
15 A2 Input Register address 2.
16 A1 Input Register address 1.
17 A0 Input Register address 0.
18 CLKIN Input Clock input. Typically 14.3 MHz. Best if driven by an ICS clock synthesizer.
19 D7 I/O Data bit 7.
20 D6 I/O Data bit 6.
21 GND Power Connect to ground.
22 VDD Power Power Supply. Connect to +5 V or +3.3 V. (Connect all VDDs to same voltage)
23 D5 I/O Data bit 5.
24 D4 I/O Data bit 4.
25 D3 I/O Data bit 3.
26 D2 I/O Data bit 2.
27 D1 I/O Data bit 1.
28 D0 I/O Data bit 0.
TOUCH SCREEN CONTROLLER
MDS 712 L 3Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Interrupts
Interrupts are controlled by register 6 (see Register Description). The INT pin (pin 2) goes high to signal an
interrupt. Interrupts are then cleared by reading any register. However, if the MK712 is in the process of
generating an interrupt during a read cycle, then the interrupt is not cleared and INT will stay high. This
internal process may take 100ns, and so to guarantee that the interrupt is cleared, two successive read
cycles may be necessary.
TOUCH SCREEN CONTROLLER
MDS 712 L 4Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
IC Operation
TOUCH SCREEN CONTROLLER
MDS 712 L 5Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Register Description
The MK712 register set is designed to be compatible with the Gazelle pen digitizer registers allowing a
software driver for the Gazelle digitizer to be used with the MicroClock MK712. The eight 8-bit registers are
defined below:
TOUCH SCREEN CONTROLLER
MDS 712 L 6Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Rate Register (Register 7) Programming
Calculating Points Per Second
The formula for determining P.P.S. is:
Power-On Reset
On application of power, an internal reset is generated that clears all bits in registers 0, 1, and 6. Register
7 is set to 32 giving a rate of 86 PPS. Note that clearing register 6 puts the IC into the power down
condition.
Initializing the MK712
The interrupt on the MK712 can only be cleared by reading a register or by writing register 6 to the power
down condition. After a fault condition, initialize the MK712 by writing register 6 to zero and then writing
register 6 to the desired value. This will always clear pending interrupts.
TOUCH SCREEN CONTROLLER
MDS 712 L 7Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Recommended Circuit
Pen Bounce
When the screen is untouched, the Y plate is driven high and the X plate is driven low. When the screen is
touched, the X plate is pulled high, which is detected by the MK712. This initiates a conversion (as long as
periodic conversions are enabled). Some de-bounce is provided by the time constant of the screen
decoupling capacitors combined with the screen resistance. However, once conversions have started, pen
bounce will not be detected until after both the X and Y points have been taken.
If the pen is lifted during a conversion, this will also not be detected until the conversion is complete. This
is typically indicated by a point with the correct Y coordinates, but minimum (for that screen) X coordinates.
Screen Decoupling
The component values suggested should give excellent results. However, for screens with a high
resistance operating at a high conversion rate, extra interrupts may be issued. This is because the time
constant of the screen decoupling capacitors and screen resistance is high, resulting in the screen
appearing to be untouched and then touched between conversions. These extra interrupts can be
eliminated by reducing the size of the screen decoupling capacitors on pins XH, XL, YH, and YL. This will,
however, slightly reduce the noise rejection, which could decrease the accuracy of the conversion.
TOUCH SCREEN CONTROLLER
MDS 712 L 8Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Optimizing Performance when Reading and Writing Registers
Reading and writing the MK712 generates digital noise that may reduce the accuracy of the A to D
converter. This noise has several causes, including board layout, data bus loading, and power supply
voltage. By appropriately timing the register operations, the effects of this noise can be minimized.
After an interrupt is issued, the MK712 allows a minimum of 1 millisecond to elapse before initiating the
conversion cycle. This allows the screen drivers to settle. For best performance, complete all register
operations within this 1ms window after an interrupt.
Power Down/Stopping the Clock
If the screen is untouched, the supply current is under 3µA. If the input clock is stopped, the supply current
is also less than 3µA. When the screen is touched with no clock, TOUCH goes low and INT goes high, but
no further operations occur until the clock starts. A to D conversions are invalid until after the clock has
stabilized at the correct frequency and one full conversion cycle has been completed.
Input Clock
The MK712 is highly tolerant of different clock frequencies (from 12 to 20 MHz), rise times, and duty cycles.
However, any input clock undershoot or overshoot will cause the MK712 to draw extra current. This can be
eliminated by using a MicroClock clock synthesizer and properly terminating the clock driver. MicroClock
makes low power clock synthesizers with 14.3 MHz power down.
Resistive Touch Screen (4-wire)
Resistive touch screens consist of 2 resistive plates that are separated by a small gap. Each plate has an
electrode at each end and when the screen is touched, the two plates are shorted together at that point.
If a voltage is applied, for example, between XL and XH, then a voltage divider is formed on the X PLATE.
When the Y PLATE is touched to the X PLATE, a voltage will be developed on the Y PLATE that is
proportional to distance of the touch from XL and XH. By accurately measuring this voltage, the position of
the touch can be determined.
TOUCH SCREEN CONTROLLER
MDS 712 L 9Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Recommended Method for Reading Points
If the user is pressing lightly on the touch screen, it is likely that the screen contact will be intermittent. The
screen will bounce, causing false points. This effect can be reduced by insuring that the screen is touched
both before and after a conversion. By doing this, the first and last point in a series of points are discarded.
The following algorithm checks that a point has valid touches both before and after a conversion, and it
distinguishes between change-in-touch interrupts and conversion complete interrupts. Register 6 bits 0, 1,
and 2 must all be true (logical 1) in order to use this method.
Warning–When Using a Switching Regulator Power Supply
When using the MK712 in a system where the power is supplied by a switching regulator, do not perform
screen conversions when the regulator is operating in the power saving mode. Some switching regulators
feature a low power mode (for example, Linear Technology’s “Burst Mode”) where the output is turned on
and off in order to save power. The extra power supply noise generated when using this mode causes
spurious data points to be returned from the MK712, so it should be disabled when the MK712 is doing
screen conversions.
TOUCH SCREEN CONTROLLER
MDS 712 L 10 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Analog to Digital Converter Option
The 12-bit ADC converts X and Y co-ordinates at a rate determined by registers 6 and 7. The converter
uses a ratiometric technique to give absolute co-ordinates on the screen, largely independent of variations
in screen resistance, temperature or power supply voltage. The total voltage applied across the screen is
defined as full-scale for the converter (i.e. 4095) and any point touched on the screen is proportional to this.
For example, if the screen is touched exactly in the center, the converter will read 2047. This feature may
allow for the elimination of calibration upon startup.
However, the full scale voltage is defined at the IC pins and so any parasitic interconnect resistance will be
included in full scale. In addition, the interconnect resistances on the screen also account for about 20% of
the total resistance. This means that approximately the bottom 10% and top 10% of full scale are
inaccessible.
The converter is guaranteed to be monotonic, with no missing codes.
TOUCH SCREEN CONTROLLER
MDS 712 L 11 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the MK712. These ratings, which
are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of the
device at these or any other conditions above those indicated in the operational sections of the
specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can
affect product reliability. Electrical parameters are guaranteed only over the recommended operating
temperature range.
Recommended Operation Conditions
Item Rating
Supply Voltage, VDD (referenced to ground) 7 V
All Inputs and Outputs (referenced to ground) -0.5 V to VDD+0.5 V
Ambient Operating Temperature (commercial) 0 to +70°C
Ambient Operating Temperature (industrial) -30 to +70°C
Ambient Operating Temperature (automotive) -35 to +85°C
Storage Temperature -65 to +150°C
Junction Temperature 125°C
Soldering Temperature (10 to 20 seconds max) 260°C
Parameter Min. Typ. Max. Units
Ambient Operating Temperature (commercial) 0 +70 °C
Ambient Operating Temperature (industrial) -30 +70 °C
Ambient Operating Temperature (automotive) -35 +85 °C
Power Supply Voltage (measured in respect to GND)
(commercial and industrial)
+3.0 +5.5 V
Power Supply Voltage (measured in respect to GND)
(automotive)
+3.135 +5.5 V
TOUCH SCREEN CONTROLLER
MDS 712 L 12 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
DC Electrical Characteristics
Unless stated otherwise,VDD = 3.3 V or 5V, TA = 0 to +70°C (commercial), -30°C to +70°C (industrial),
-35°C to +85°C (automotive)
Parameter Symbol Conditions Min. Typ. Max. Units
Operating Voltage VDD Commercial and
industrial
3.0 5.5 V
Operating Voltage VDD Automotive 3.135 5.5 V
Input High Voltage VIH VDD=5 V 2 V
Input Low Voltage VIL VDD=5 V 0.8 V
Output High Voltage VOH IOH = -2 mA VDD-0.4 V
Output High Voltage VOH VDD=5 V,
IOH = -12 mA
2.4 V
Output Low Voltage VOL VDD=5 V,
IOL = 12 mA
0.4 V
Input High Voltage VIH VDD=3.3 V 1.9 V
Input Low Voltage VIL VDD=3.3 V 0.4 V
Output High Voltage VOH VDD=3.3 V,
IOH = -8 mA
2.4 V
Output Low Voltage VOL VDD=3.3 V,
IOL = 8 mA
0.4 V
Operating Supply Current IDD At VDD=5 V, 300Ω
screen, 100 PPS
5mA
At VDD=3.3 V, Note 3 3 mA
Standby, Clock, Note 4 0.5 3 µA
Standby, Note 5 0.5 3 µA
Power down, PD=0 or
PD=1, no clock
0.2 3 µA
Short Circuit Current IOS Each output ±50 mA
Input Capacitance CIN 7pF
TOUCH SCREEN CONTROLLER
MDS 712 L 13 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
AC Electrical Characteristics
Unless stated otherwise,VDD = 3.3 V or 5 V, TA = 0 to +70°C (commercial), -30°C to +70°C (industrial),
-35°C to +85°C (automotive)
Note 1: Consult with ICS about the best device to use to generate the input clock.
Note 2: With no missing codes.
Note 3: Assumes no 14.3 MHz input clock overshoot, 300Ω screen, 100 PPS.
Note 4: Assumes no 14.3 MHz input clock overshoot, no touch.
Note 5: With no touch, no clock.
Parameter Symbol Conditions Min. Typ. Max. Units
Input Clock Frequency, pin 18 Note 1 12 14.32 20 MHz
Input Clock Duty Cycle, pin 18 At 1.5 V 25 75 %
Output Rise Time tOR 0.8 to 2.0 V, VDD=5 V 3 ns
Output Fall Time tOF 2.0 to 0.8 V, VDD=5 V 3 ns
Resolution 12 bits
Non-linearity Monotonic, Note 2 ±2 LSB
Touch Screen Resistance 100 2000 Ω
TOUCH SCREEN CONTROLLER
MDS 712 L 14 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Register Interface Timing
Notes:
1. RD edges may precede or follow CS edges.
2. WR edges may precede or follow CS edges.
3. Either TRDW or TRDWC specification must be met.
4. Either TRDHW or TRDHWC specification must be met.
5. It is not permitted to have both RD and WR low at the same time.
Number Symbol Description Min. Max. Units Note
Read and Write Cycles
1 TRASC Address Setup to CS Low 5 ns
2 TRAHC Address Hold from CS High 0 ns
3 TRCCY CS High to CS Low 40 ns
Read Cycle Only
4 TRSCR CS Low to RD Low 10 ns
5 TRRD RD Pulse Width 40 ns
6 TRCHR1 RD High to CS High 0 ns
7 TRCHR2 RD High to CS Low 40 ns
8 TRDC CS Low to Data 35 ns
9 TRDR RD Low to Data 35 ns
10 TRDHC CS High to Data Release 2 20 ns 1
11 TRDHR RD High to Data Release 2 20 ns 1
Write Cycle Only
12 TRCSW CS Low to WR Low 10 ns
13 TRWR WR Pulse Width 40 ns
14 TRCHW WR High to CS High 0 ns 2
15 TRWH WR High to CS Low 40 ns
16 TRWCY WR High to WR Low 40 ns
17 TRDW Data Setup to WR High 15 ns 3
18 TRDHW Data Hold from WR High 15 ns 4
19 TRDWC Data Setup to CS High 15 ns 3
20 TRDHWC Data Hold from CS High 15 ns 4
TOUCH SCREEN CONTROLLER
MDS 712 L 15 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Register Read
Register Write
TOUCH SCREEN CONTROLLER
MDS 712 L 16 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Touchscreen Resistance Graph 1
Touchscreen Resistance Graph 2
TOUCH SCREEN CONTROLLER
MDS 712 L 17 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Touchscreen Resistance Graph 3
TOUCH SCREEN CONTROLLER
MDS 712 L 18 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Suggested Layout
Notes:
1. The 14.318 MHz input clock on pin 18 should have a 33Ω series termination resistor at its source.
Consult ICS for the best way to generate this clock.
2. All digital signals should be kept well away from pins 4, 5, 6, 7, 8, 9, 10, and 11, and any traces
connected to those pins.
TOUCH SCREEN CONTROLLER
MDS 712 L 19 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Package Outline and Package Dimensions (28-pin SOIC, 300 Mil. Wide Body)
Package dimensions are kept current with JEDEC Publication No. 95
INDEX
AREA
1 2
28
D
E
SEATING
PLANE
A1
A
e
- C -
B
.10 (.004) C
C
L
H
h x 45
Millimeters Inches
Symbol Min Max Min Max
A — 2.65 — 0.104
A1 0.10 — 0.004 0.010
A2 -- 1.50 0.0040 —
B 0.33 0.51 0.013 0.020
C 0.18 0.32 0.007 0.013
D 17.70 18.40 0.697 0.724
E 7.40 7.60 0.291 0.299
e 1.27 Basic .050 Basic
H 10.00 10.65 0.394 0.419
h 0.25 0.75 0.010 0.029
L 0.40 1.27 0.016 0.050
α0°8°0°8°
TOUCH SCREEN CONTROLLER
MDS 712 L 20 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Package Outline and Package Dimensions (28-pin SSOP, 150 Mil. Wide Body)
Package dimensions are kept current with JEDEC Publication No. 95
INDEX
AREA
1 2
28
D
E1 E
SEATING
PLANE
A
1
A
A
2
e
- C -
b
aaa C
c
L
Millimeters Inches
Symbol Min Max Min Max
A 1.35 1.75 0.053 0.069
A1 0.10 0.25 0.004 0.010
A2 -- 1.50 -- .059
b 0.20 0.30 0.008 0.012
C 0.18 0.25 0.007 0.010
D 9.80 10.00 0.386 0.394
E 5.80 6.20 0.228 0.244
E1 3.80 4.00 0.150 0.157
e .635 Basic .025 Basic
L 0.40 1.27 0.016 0.050
α0°8°0°8°
TOUCH SCREEN CONTROLLER
MDS 712 L 21 Revision 070805
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK712
Ordering Information
Parts that are ordered with a “LF” suffix to the part number are the Pb-Free configuration and are RoHS compliant.
While the information presented herein has been checked for both accuracy and reliability, Integrated Circuit Systems (ICS)
assumes no responsibility for either its use or for the infringement of any patents or other rights of third parties, which would
result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial
applications. Any other applications such as those requiring extended temperature range, high reliability, or other extraordinary
environmental requirements are not recommended without additional processing by ICS. ICS reserves the right to change any
circuitry or specifications without notice. ICS does not authorize or warrant any ICS product for use in life support devices or
critical medical instruments.
Part / Order Number Marking Shipping Packaging Package Temperature
MK712S MK712S Tubes 28-pin SOIC 0 to +70° C
MK712STR MK712S Tape and Reel 28-pin SOIC 0 to +70° C
MK712SI MK712SI Tubes 28-pin SOIC -30 to +70° C
MK712SITR MK712SI Tape and Reel 28-pin SOIC -30 to +70° C
MK712R MK712R Tubes 28-pin SSOP 0 to +70° C
MK712RTR MK712R Tape and Reel 28-pin SSOP 0 to +70° C
MK712RLF MK712RLF Tubes 28-pin SSOP 0 to +70° C
MK712RLFTR MK712RLF Tape and Reel 28-pin SSOP 0 to +70° C
MK712RI MK712RI Tubes 28-pin SSOP -30 to +70° C
MK712RITR MK712RI Tape and Reel 28-pin SSOP -30 to +70° C
MK712RWLF MK712RWLF Tubes 28-pin SSOP -35 to +85° C
MK712RWLFTR MK712RWLF Tape and Reel 28-pin SSOP -35 to +85° C
