LM8300IMT9 - National Semiconductor

LM8300/LM8500

Four Wire Resistive Touchscreen Controller with

Brownout

1.0 General Description

The LM8300/8500 is a 4-wire resistive touch screen control-

ler. The controller samples and drives the touch screen

without the need of any external hardware. The built in 10-bit

A/D provides a maximum of 500 coordinate pairs per second

(cpps). The data sampled from the touch screen is sent out

on the UART at a speed of 38400 bps.

The controller has a power-saving mode which causes the

controller to self-power down when no touch is detected on

the touch screen for a specified amount of time. In the

self-power down mode, the current drawn is typically less

than 2 µA. The device resumes normal operation when a

touch is detected on the touch screen or communication is

detected on the UART. In addition to the self-power down

mode, the controller can be disabled by pulling the SHUT-

DOWN pin low. The controller resumes normal operation

when the SHUTDOWN pin is tristated or pulled high.

The controller has an internal non-volatile memory storage

element to store configuration data such as calibration points

or controller configurations.

Devices included in this datasheet:

Device Operating

Voltage

Brownout

Voltage

Operating

Frequency

I/O

Pins Packages Temperature

LM8300 3, 5 V 2.7 to 2.9 V 3.27 MHz 18 44 LLP, 44 PLCC,

48 TSSOP 0˚C to +70˚C

LM8500 5 V 4.17V to 4.5V 3.27, 10 MHz 18 44 LLP, 44 PLCC,

48 TSSOP 0˚C to +70˚C

2.0 Features

KEY FEATURES

nSupports 4 wire resistive touch panels

nLow power standby current typically less than 2 µA at

5.5V

nMaximum speed of 500 coordinate pairs per second

nAutomatic wake up and return to standby

n10 bit A/D

nOn-chip touch screen current drivers - no external driver

required

nUART interface

nController configurations are stored in the internal

non-volatile storage element

nTouch pressure can be measured

APPLICATIONS

nPersonal Digital Assistants

nSmart Hand-Held Devices

nTouch Screen Monitors

nPoint-of-Sales Terminals

nKIOSK

nPagers

nCell Phones

COP8™is a trademark of National Semiconductor Corporation.

PRELIMINARY

December 2003

LM8300/LM8500 Four Wire Resistive Touchscreen Controller with Brownout

3.0 Block Diagram

20037201

* This pin is available in the LM8500. It is unused in the LM8300.

4.0 Ordering Information

Part Numbering Scheme

LM 8300 H VA 9

Family and Feature Set Indicator No. Of Pins Package Type Temperature

8300 = Low Brownout Voltage

8500 = High Brownout Voltage

H=44Pin

I=48Pin

LQ = LLP

MT = TSSOP

VA = PLCC

9=0to+70˚C

LM8300/LM8500

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Table of Contents

1.0 General Description ..................................................................................................................................... 1

2.0 Features ....................................................................................................................................................... 1

3.0 Block Diagram .............................................................................................................................................. 2

4.0 Ordering Information .................................................................................................................................... 2

5.0 Connection Diagrams ................................................................................................................................... 4

6.0 Pin Descriptions ........................................................................................................................................... 5

7.0 Absolute Maximum Ratings ......................................................................................................................... 7

8.0 Electrical Characteristics .............................................................................................................................. 7

9.0 Functional Description .................................................................................................................................. 8

9.1 GENERAL ................................................................................................................................................. 8

9.2 ADVANCED PIN DESCRIPTIONS ............................................................................................................ 8

9.3 USART FRAMING FORMAT ..................................................................................................................... 9

9.3.1 Data packet format table ..................................................................................................................... 9

9.3.2 Command Bytes .................................................................................................................................. 9

9.3.3 Advanced Command Bytes Descriptions .......................................................................................... 10

10.0 Oscillator .................................................................................................................................................. 12

11.0 Power Save Mode (Low Power Stand-by) ............................................................................................... 13

12.0 Averaging Algorithm ................................................................................................................................. 13

12.1 DELTA ALGORITHM ............................................................................................................................. 13

12.2 FOCUS ALGORITHM ............................................................................................................................ 14

12.3 COMMUNICATION MODES ................................................................................................................. 14

13.0 Brownout Reset ........................................................................................................................................ 14

14.0 Calibration ................................................................................................................................................ 15

14.1 GENERAL CALIBRATION PROCEDURES .......................................................................................... 16

14.2 CALIBRATION PROCEDURES WITH COORDINATES CHECKING ENABLED ................................. 17

14.3 CALIBRATION PROCEDURES WITH COORDINATES CHECKING DISABLED ................................ 18

15.0 Revision History ....................................................................................................................................... 18

16.0 Physical Dimensions ................................................................................................................................ 19

LM8300/LM8500

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5.0 Connection Diagrams

20037202

* This pin is available in the LM8500. It is unused in the LM8300.

Top View

Plastic Chip Package

See NS Package Number V44A

20037203

* This pin is available in the LM8500. It is unused in the LM8300.

Top View

LLP Package

See NS Package Number LQA44A

20037204

* This pin is available in the LM8500. It is unused in the LM8300.

Top View

TSSOP Package

See NS Package Number MTD48

LM8300/LM8500

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6.0 Pin Descriptions

Pinouts for 44- and 48-Pin Packages

Pin Name Direction Pin Description 44-Pin LLP 44-Pin PLCC 48-Pin TSSOP

RESET I Reset pin, pull low to reset 6 1 1

DTR I UART data terminal ready signal 7 2 2

WD_OUT OWatchdog output, tie to RESET pin

for correct function

833

CLK_SET

IUsed to set if crystal is 3.3 MHz (low)

or 10 MHz (floating or pulled high)

944

Unused

10 5 5

Unused

11 6 6

Unused

12 7 7

Unused

13 8 8

OSC_OUT O Clock oscillator output 14 9 9

OSC_IN I Clock oscillator input 15 10 10

Unused

16 11 11

Unused

17 12 12

UART_TX O UART transmit pin (inverted for use

with standard RS-232 drivers)

18 13 13

UART_RX I UART receive pin (inverted for use

with standard RS-232 drivers

19 14 14

SHUTDOWN I Shutdown pin, puts the device in halt

mode if pulled low

20 15 15

Unused

21 16 16

Unused

22 17 17

WAKE-UP I Used to wake up the processor from

halt mode with touch on touch screen

23 18 18

X+ I/O Drives the X+ wire, also analog input

when sampling

24 19 19

Y- I/O Drives the Y- wire, also analog input

when sampling

25 20 20

X- I/O Drives the X- wire, also analog input

when sampling

26 21 21

Y+ I/O Drives the Y+ wire, also analog input

when sampling

27 22 22

Unused

28 23 23

Unused

29 24 24

FILTER_OUT O Analog output to the filter 30 25 25

FILTER_IN I Analog input from the filter 31 26 26

GND Digital ground 32 27 27

AGND Analog ground 33 28 28

Analog power supply, connect to filter

for best performance

34 29 31

Digital power supply 35 30 32

Unused

XX33

Unused

XX34

Unused

36 31 35

Unused

37 32 36

Unused

38 33 37

Unused

39 34 38

Unused

40 35 39

Unused

41 36 40

LM8300/LM8500

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6.0 Pin Descriptions (Continued)

Pinouts for 44- and 48-Pin Packages (Continued)

Pin Name Direction Pin Description 44-Pin LLP 44-Pin PLCC 48-Pin TSSOP

LED Output Optional LED output, low when

running, high in halt-mode

42 37 41

Unused

34246

Unused

44347

Unused

54448

Note 1: This is available in the LM8500 only.

Note 2: These pins are for future functional expansions.

LM8300/LM8500

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7.0 Absolute Maximum Ratings (Note

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage (V

)7V

Voltage at Any Pin −0.3V to V

+0.3V

Total Current into V

Pin (Source) 200 mA

Total Current out of GND Pin (Sink) 200 mA

Storage Temperature Range −65˚C to +140˚C

ESD Protection Level 2 kV (Human Body

Model)

Note 3: Absolute maximum ratings indicate limits beyond which damage to

the device may occur. DC and AC electrical specifications are not ensured

when operating the device at absolute maximum ratings.

8.0 Electrical Characteristics

DC Electrical Characteristics (0˚C ≤T

≤+70˚C)

Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Parameter Conditions Min Typ Max Units

Operating Voltage 2.7 5.5 V

Power Supply Rise Time 10 50 x 10

Power Supply Ripple (Note 4) Peak-to-Peak 0.1 V

Supply Current (Note 5)

High Speed Mode

CKI = 10 MHz V

= 5.5V 11.5 mA

CKI = 3.33 MHz V

= 4.5V 5 mA

HALT Current with BOR Disabled (Note 6)

High Speed Mode V

= 5.5V, CKI=0MHz <210µA

Supply Current for BOR Feature V

= 5.5V 45 µA

High Brownout Trip Level (BOR Enabled) 4.17 4.28 4.5 V

Low Brownout Trip Level (BOR Enabled) 2.7 2.78 2.9 V

Input Levels (V

)

Logic High 0.8 V

Logic Low 0.16 V

Internal Bias Resistor for the CKI

Crystal/Resonator Oscillator 0.3 1.0 2.5 MΩ

Hi-Z Input Leakage V

= 5.5V −0.5 +0.5 µA

Input Pullup Current V

= 5.5V, V

= 0V −50 −210 µA

Port Input Hysteresis 0.25 V

Output Current Levels

Outputs X+, X-, Y+, Y-

Source (Note 7) V

= 4.5V, V

= 4.2V −10 mA

= 2.7V, V

= 2.4V −6 mA

Sink (Note 7) V

= 4.5V, V

= 0.3V 10 mA

= 2.7V, V

= 0.3V 6 mA

Allowable Sink and Source Current per Pin 20 mA

All Others

Source (Weak Pull-Up Mode) V

= 4.5V, V

= 3.8V −10 µA

= 2.7V, V

= 1.8V −5 µA

Source (Push-Pull Mode) V

= 4.5V, V

= 3.8V −7 mA

= 2.7V, V

= 1.8V −4 mA

Sink (Push-Pull Mode) (Note 7) V

= 4.5V, V

= 1.0V 10 mA

= 2.7V, V

= 0.4V 3.5 mA

Allowable Sink and Source Current per Pin 15 mA

TRI-STATE Leakage V

= 5.5V −0.5 +0.5 µA

Maximum Input Current without Latchup ±200 mA

RAM Retention Voltage, V

(in HALT Mode) 2.0 V

LM8300/LM8500

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8.0 Electrical Characteristics (Continued)

DC Electrical Characteristics (0˚C ≤T

≤+70˚C) (Continued)

Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Parameter Conditions Min Typ Max Units

Input Capacitance 7pF

Note 4: Maximum rate of voltage change must be <0.5 V/ms.

Note 5: Supply and IDLE currents are measured with CKI driven with a

square wave Oscillator, CKO driven 180˚ out of phase with CKI, inputs

connected to VCC and outputs driven low but not connected to a load.

Note 6: The HALT mode will stop CKI from oscillating. Measurement of IDD

HALT is done with device neither sourcing nor sinking current; all inputs tied

to VCC; A/D converter and clock monitor and BOR disabled.

Note 7: Absolute Maximum Ratings should not be exceeded.

A/D Converter Electrical Characteristics (0˚C ≤T

≤+70˚C) (Single-ended

mode only)

Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Parameter Conditions Min Typ Max Units

Resolution 10 Bits

DNL V

=5V ±1 LSB

DNL V

=3V ±1 LSB

INL V

=5V ±2 LSB

INL V

=3V ±4 LSB

Offset Error V

=5V ±1.5 LSB

Offset Error V

=3V ±2.5 LSB

Gain Error V

=5V ±1.5 LSB

Gain Error V

=3V ±2.5 LSB

Input Voltage Range 2.7V ≤V

<5.5V 0 V

Analog Input Leakage Current 0.5 µA

Analog Input Resistance (Note 8) 6k Ω

Analog Input Capacitance 7pF

Operating Current on AV

= 5.5V 0.2 0.6 mA

Note 8: Resistance between the device input and the internal sample and hold capacitance.

9.0 Functional Description

9.1 GENERAL

The LM8300/8500 is a 4-wire resistive touch screen control-

ler. The primary communication is through the built in UART

operating at a baud rate of 38400. The LM8300/8500 has the

ability to measure pressure on the Z-axis, in addition to the

X-Y coordinates.

The device has the capability to do a 2, 5, and 13 point

calibration. All calibration data is stored in the internal non-

volatile storage element. In addition, all settings pertaining to

the controller are stored internally. This feature negates the

need for external EEPROM.

The device has three built in averaging algorithms: oversam-

pling, delta, and focus. These algorithms help to minimize

noise and A/D variation due to noise. Refer to the averaging

algorithm section for a more detail explanation. These algo-

rithms are implemented on-chip, freeing the main processor

from these tasks. To further minimize noise in extremely

noisy environments, the device has the ability to route the

signal from the touch panel to an external filtering stage

before A/D conversions are performed.

To minimize power consumption, the device can be put into

power save mode. The device can be set to go into power

save mode automatically or manually by pulling the external

shutdown pin low.

9.2 ADVANCED PIN DESCRIPTIONS

CLK_SET — This pin is the selection pin used to determine

the operating frequency of the controller. On power up, the

controller polls this pin to determine if the operating fre-

quency is set to 10 MHz or 3.3 MHz. If the pin is left floating

or tied high, then the operating frequency is 10 MHz. If the

pin is tied low, then the operating frequency is set to 3.3

MHz.

Note: This is available on the LM8500 only.

SHUTDOWN — This is the external shut down pin. When

pulled low, the controller goes into power saving mode. This

selection pin state has higher priority than the internal power

save mode settings.

WAKE_UP — This pin is used to wake the controller from

power save mode. When the device is in power save mode,

the pin must be tied to one of X-Y lines coming from the

touch screen panel.

X+ — Connect to X+ terminal of the resistive screen.

X- — Connect to X- terminal of the resistive screen.

Y+ — Connect to Y+ terminal of the resistive screen.

Y- — Connect to Y- terminal of the resistive screen.

Filter_out — Analog output to external filter. The use of the

external filter is controlled by sending a command byte of

$A0 on the UART to the controller.

Filter_in — Analog input from external filter. The use of the

external filter is controlled by sending a command byte of

$A0 on the UART to the controller.

LM8300/LM8500

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9.0 Functional Description (Continued)

LED — Optional LED output. When the controller is oper-

ating in normal (non power save) mode, a low is output to the

pin. When the controller is in power save mode, a high is

output to the pin.

RESET — Reset pin. When pulled low, a manual reset is

executed. For normal operation, this pin must be pulled high.

Under no circumstances should the pin be left floating.

UART_TX — UART transmit pin. The signal is inverted for

use with standard RS-232 drivers.

UART_RX — UART receive pin. The signal is inverted for

use with standard RS-232 drivers.

DTR — Data Terminal Ready signal for the UART. If a high

level is detected on the pin, this signals that the UART is not

ready. If a low level is detected on the pin, this signals that

the UART is ready.

WD_Out — Watch dog output. For correct operation, this

pin should be connected to the RESET pin.

OSC_OUT — Clock oscillator output pin.

OSC_IN — Clock oscillator input pin

GND — Digital Ground

AGND — Analog ground

— Digital power supply.

— Analog power supply. For best performance, this

pin should be connected to a filter.

Users of the LLP package are cautioned to be aware that the

central metal area and the pin 1 index mark on the bottom of

the package may be connected to GND. See figure below:

9.3 USART FRAMING FORMAT

The device communicates with the touch screen driver using

the UART set at a baud rate of 38400, 8, n, 1.

All communication from the host software and the controller

consists of a command byte and occasionally data byte(s). If

data byte(s) follow a command byte, it must be sent directly

after the command byte. If the device is in the power save

mode, a delay must be inserted between the wake up com-

mand and the command byte. Refer to the Power Save

mode section for more details. For every command byte sent

to the controller, an acknowledge byte is sent back and

sometimes data byte(s).

A command byte is distinguished by having the 7th bit of the

command byte set (1). If any data byte(s) is to follow, the 7th

bit of the data byte is reset (0).

Data packets sent to the host software can be either four or

five bytes in length. If the pressure measurement is enabled,

five bytes are sent. If the pressure measurement is not

enabled, four bytes are sent.

The first byte of each data packet is a header byte. This

header byte is used to synchronize and differentiate between

four or five byte packages. If a four byte data package is

sent, the 4th bit of the header byte is reset (0). If a five byte

data package is sent, the 4th bit of the header byte is set (1).

The 6th bit of the second byte of the data packet is used to

indicate the touch state. If the bit is set (1), then a touchdown

or continuous touch is detected. If the bit is reset (0), then a

liftoff is detected.

9.3.1 Data packet format table

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

Byte 1 1 0 0 L 0 0 0 0

Byte 2 0 S X

Byte 3 0 X

Byte 4 0 Y

Byte 5 0 Z

L - Package length. (0 = 4 bytes,1=5bytes)

S - Touch state (0 = liftoff, 1 = touchdown or continuous

touch)

- X position (10 bit value)

- Y position (10 bit value)

- Z positon (7 bit value), this byte is only transmitted if the

pressure measurement is enabled

9.3.2 Command Bytes

Command

Byte

Byte 2

TSC

Byte 1

TSC

Byte 2

Read

clock-speed

(3,33MHz,

10MHz)

$B0 $CA $00, $01

Read

parameters

$B1 $CA Section

9.3.3

Advanced

Command

Bytes

Descriptions

Read

software

version

number

$B2 $C7 Section

9.3.3

Advanced

Command

Bytes

Descriptions

Read # of

calibration

points

$B3 $CA $00, $02,

$05, $0D

20037216

FIGURE 1. LLP Package Bottom View

LM8300/LM8500

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9.0 Functional Description (Continued)

Command

Byte

Byte 2

TSC

Byte 1

TSC

Byte 2

Read stored

calibration

points

$B4 $CA Section

9.3.3

Advanced

Command

Bytes

Descriptions

Set focus

value (# of

pixels on

touch panel)

$B8 $0-$3F $CA $00-$3F

Set#of

samples per

coordinate (1,

2, 4, 8, 16,

32)

$BA $01, $02,

$04, $08,

$10, $20

$CA $01, $02,

$04, $08,

$10, $20

Set

communication

mode

(stream,

touchdown,

liftoff)

$BB $01, $02,

$04

$CA $01, $02,

$04

Set max delta

(# of pixels

from

predicted

coordinate)

$BC $00-$3F $CA $00-$3F

Set calibration

points

$BD Section

9.3.3

Advanced

Command

Bytes

Descriptions

$CA Section

9.3.3

Advanced

Command

Bytes

Descriptions

Set minimum

pressure

$BE $00-$7F $CA $00-$7F

Toggle

disable/enable

external filter

path

$A0 $CA $00, $01

Toggle

disable/enable

self

power-down

$A2 $CA $00, $01

Toggle

disable/enable

echo mode

$A3 $CA $00, $01

Toggle

disable/enable

pressure

measurements

$A4 $CA $00, $01

Command

Byte

Byte 2

TSC

Byte 1

TSC

Byte 2

Toggle

disable/enable

calibration

coordinate

check

$A5 $CA $00, $01

Wakeup $A7

Shutdown $A8 $CA

Soft reset $AF $CA $CB, $CC

TSC Replies

Timeout $CF

Re-send $CE

Self test failed $CC

Self test ok $CB

Acknowledge $CA

Calibration

coordinates

$C4

Error / buffer

overrun

$C8

Software

version

$C7 $0-$7F

Data transmit $80/$90 Payload (3/4

bytes)

9.3.3 Advanced Command Bytes Descriptions

Unless otherwise mentioned, all values are in hex.

$B0: Read clock-speed

Reply Byte #1: $CA (Acknowledge)

Byte #2: Clock readout (0 = 3.3MHz, 1 = 10MHz)

CLK_SEL pin tells the firmware which oscillator speed is

used. If the CLK_SEL input pin is floating or pulled high a

10.0MHz oscillator must be connected. If the pin is pulled

low a 3.3MHz oscillator must be connected. This command

enables the driver software to determine which oscillator

speed is used with the touch screen controller, as this deter-

mines the maximum coordinate pair per second data rates.

Note: This is available in the LM8500 only.

$B1: Read parameters

Reply Byte #1: $CA (Acknowledge)

Reply Byte #2: First byte in software version number,

year 20 (00-99)

Reply Byte #3: Communication mode (1 = stream, 2 =

touchdown, 4 = liftoff)

Byte #4: Wakeup on touch (0 = disabled, 1 = enabled)

Reply Byte #5: Number of samples (1,2, 4, 8, 16 or

32)

Byte #6: Clock readout (0 = 3.3MHz, 1 = 10MHz)

Byte #7: Second byte in software version number,

month (1-12)

Byte #8: Third byte in software version number, day

(1-31)

Byte #9: Focus value (0-63)

Byte #10: Max delta (0-63)

LM8300/LM8500

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9.0 Functional Description (Continued)

Byte #11: Number of calibration coordinates (0, 2, 5 or

13)

Byte #12: Toggle-flags:

Bit #5: calibration coordinates check (0=disabled,

1=enabled)

Bit #4: Pressure measurement (0=disabled,

1=enabled)

Bit #3: Echo mode (0=disabled, 1=enabled)

Bit #2: Self Power-Down mode (0=disabled,

1=enabled)

Bit #1: Unused

Bit #0: External filter path (0=disabled, 1=enabled)

Byte #13: Pressure threshold for valid touch

This command allows the user to read all the selected pa-

rameters. It is primary intended to aid in debugging. This

command can also be used if a configuration utility needs to

determine the current setting of controller.

$B2: Read software version number

Reply Byte #1: $C7 (Software version number)

Byte #2: First byte in version number, year 20 (00-99)

Byte #3: Second byte in version number, month (1-12)

Byte #4: Third byte in version number, day (1-31)

$B3: Read # of calibration points

Reply Byte #1: $CA (Acknowledge)

Byte #2: ($00 — no calibration done, $02 — 2 points,

$05 — 5 points or $0D — 13 points)

$B4: Read stored calibration points

Reply Byte #1: $CA (Acknowledge)

Byte #2: ($00 — no calibration done, $02 — 2 points,

$05 — 5 points or $0D — 13 points)

Byte #3: X-max (2 MSB for coordinate 1)

Byte #4: X-min (8 LSB for coordinate 1)

Byte #5: Y-max (2 MSB for coordinate 1)

Byte #6: Y-min (8 LSB for coordinate 1)

Continue until all coordinates have been sent. A zero is send

back if calibration has not been performed and there are no

data bytes.

$B8: Set focus value

Byte #2: Focus value (0-63)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Focus value (0-63)

The set focus command allows the setting of different values

to improve touch screen focusing. Focusing is defined as the

ability of the touch screen controller to detect exactly identi-

cal coordinate values from measurement to measurement if

the pointer on the touch screen has not moved. The focus

values are equivalent to pixels of touch screen resolution. If

for example a value of 2 is selected, this means that every

coordinate value that is within two pixels of the previously

measured coordinate value is considered to be identical to

that previous value and that in this case the touch screen

controller transmits the previous coordinate information. This

keeps the mouse pointer steady at the point being touched,

rather than "jumping around" the point. A Focus value of zero

disables the focusing algorithm. The default setting is 4.

$BA: Set number of samples per coordinate

Byte #2: Number of samples per coordinate ($01 - 1

samples/coordinate, $02 - 2 samples/coordinate, $04

- 4 samples/coordinate, $08 - 8 samples/coordinate,

$10 - 16 samples/coordinate, $20 - 32

samples/coordinate)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Number of samples per coordinate ($01 - 1

samples/coordinate, $02 - 2 samples/coordinate, $04 -

4 samples/coordinate, $08 - 8 samples/coordinate,

$10 - 16 samples/coordinate, $20 - 32

samples/coordinate)

This command allows the selection of different sample num-

bers per X, Y, and Z coordinates. The higher the number of

samples per X, Y, and Z coordinates, the better the accuracy,

but the lower the coordinates per second data rate. The

default setting is 8.

$BB: Set communication mode

Byte #2: Communication mode ($01 = stream, $02 =

touchdown, $04 = liftoff)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Communication mode ($01 = stream, $02 =

touchdown, $04 = liftoff)

See the communication modes section for a description of

the stream, touchdown and liftoff modes. This command

selects the communication mode. The default setting is

stream mode.

$BC: Set max delta

Byte #2: Max delta value (0-63)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Max delta value (0-63)

See the averaging algorithms section for a detailed descrip-

tion of this setting. Simply put, this command sets how much

the "coordinate velocity" can change from one coordinate to

the next. The default setting is 8.

$BD: Set calibration points

Byte #2: High nibble: Number of calibration points

($01 = two, $02 = five, $04 = thirteen)

Low nibble: Active calibration cross (1-13 = cross #)

Reply Byte #1: $CA (Acknowledge)

Byte #2: High nibble: Number of calibration points

($01=two, $02=five, $04=thirtheen)

Low nibble: Active calibration cross # (1-13)

Refer to the calibration section for details.

$BE: Set minimum pressure

Byte #2: Minimum pressure value (0-127)

Reply Byte #1: $CA (Acknowledge)

Byte #2: Minimum pressure value (0-127)

This setting controls how high the pressure (Z-axis) must be

in order for samples to be accepted. Setting this value too

low may result in having faulty coordinates accepted. This

value is internally multiplied by two in the controller (due to

the 7-bit limitation in the communication format, which can

not send 8-bit values larger than 127 in one byte). The

default setting is 40.

$A0: Toggle disable/enable external filter path

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

This command enable/disable external filter path. The exter-

nal filter path enabled option will require the addition of a

single external low pass filter (either R/C or active OpAmp

based), which is then applied to the touch screen signal

LM8300/LM8500

www.national.com11

9.0 Functional Description (Continued)

lines. This option can be used in high noise environments to

significantly improve performance and accuracy of the touch

screen controller.

The default setting is filter path enabled.

$A2: Toggle disable/enable self-power down

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

This command can switch between self-power down mode

enable or disabled. Refer to the Power Save Mode section

for details. The default setting is Self-Power Down mode

enabled. If the echo mode is enabled, any command byte

send to the device will be echo back and executed.

$A3: Toggle disable/enable echo mode

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

The echo mode is available for debugging purposes. If en-

abled, the touch screen controller will echo back any data

that is received via the UART interface.

The default setting is Echo mode disabled.

$A4: Toggle disable/enable pressure measurement

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

The pressure measurement sets the touch screen to also

sample the Z-axis when reading the X and Y coordinates.

The default setting is pressure measurement enabled.

$A5: Toggle disable/enable calibration checking.

Reply Byte #1: $CA (Acknowledge)

Byte #2: (0 = now disabled, 1 = now enabled)

If the cablibration checking is enabled, the cablibration map-

ping must be the values shown in ??? to ???.

$A7: Wakeup

There is no reply byte to this command.

When the self-power down mode of the device is enabled,

the touch screen driver must send a wakeup command prior

to any command byte(s). If the self-power down mode of the

TSC is enabled. The wakeup command must also to be sent

if the driver puts the TSC in power-down mode via the

shutdown command.

$A8: Shutdown

Reply Byte #1: $CA (Acknowledge)

When the TSC driver wants the controller to go into power

save mode it sends a shutdown command to the controller.

The driver needs to send a wakeup to the controller before

starting up the communication again.

With the TSC has the self-power-down mode enabled, then

a touchdown on the touch screen will wake-up the TSC from

shutdown mode in addition to sending the wake up com-

mand. If the self-power-down mode is disabled, then only the

wakeup command can wake-up the controller from shut-

down mode (i.e. wake-up on touchdown is disabled).

$AF: Soft reset (restart the controller)

Reply Byte #1: $CA (Acknowledge)

Byte #2: $CB/$CC (Self test OK/Self test fail)

When the PC driver sends the soft reset command, the

touch screen controller executes a soft reset, which clears

and re-initializes all internal RAM configuration registers

from on-chip FLASH and performs a self-check of internal

RAM and program memory.

CONTROLLER REPLIES

$CF: Timeout.

Communication timeout has occurred, and current command

has been aborted.

$CE: Re-send

Request the TSC driver to resend the last command. This

command is used if the controller does not understand the

received command or a buffer overrun condition occurs.

$CC: Self test fail (done at startup, reset, and after

calibration)

$CB: Self test OK (done at startup, reset, and after

calibration)

$CA: Acknowledge

$C4: Calibration coordinates OK

This is sent if the coordinates are within the predefined

value.

$C8: Error / TX Buffer overrun

This is added to the last place in transmit buffer to signal that

a buffer overrun has occurred.

$C7: Software Version number

Byte #2: First byte of version number

Byte #3: Second byte of version number

Byte #4: Third byte of version number

$80: Format tablet for Z-axis disabled (see Format Table

section for more info.)

Byte #2: Status, low X and low Y

Byte #3: High X

Byte #4: High Y

$90: Format tablet for Z-axis enabled (see Format Table

section for more info.)

Byte #2: Status, low X and low Y

Byte #3: High X

Byte #4: High Y

Byte #5: Z-axis (0-127)

10.0 Oscillator

OSC_IN is the clock input while OSC_OUT is the clock

generator output to the crystal. Table 1. Crystal Oscillator

Configuration,

= 25˚C, V

=5Vshows the component values required

for various standard crystal values. Figure 2 shows the

crystal oscillator connection diagram.

20037215

FIGURE 2. Crystal Oscillator

LM8300/LM8500

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10.0 Oscillator (Continued)

TABLE 1. Crystal Oscillator Configuration,

= 25˚C, V

=5V

C1 (pF) C2 (pF) CKI Freq.

(MHz)

18 18 10

18–36 18–36 3.27

The crystal and other oscillator components should be

placed in close proximity to the OSC_IN and OSC_OUT pins

to minimize printed circuit trace length.

The values for the external capacitors should be chosen to

obtain the manufacturer’s specified load capacitance for the

crystal when combined with the parasitic capacitance of the

trace, socket, and package (which can vary from 0 to 8 pF).

The guideline in choosing these capacitors is:

Manufacturer’s specified load cap = (C

)/(C

parasitic

can be trimmed to obtain the desired frequency. C

should be less than or equal to C

11.0 Power Save Mode (Low Power

Stand-by)

The power consumption of the controller can be minimized

by enabling the low power stand by mode. The power save

mode can be controlled internally by sending a command of

$A2 to the controller, externally by pulling the SHUTDOWN

pin low, or by issuing a driver shutdown command of $A8.

The self power down mode is enabled/disabled by sending a

command of $A2 to the controller. When enabled, the con-

troller automatically goes into low power stand by if no more

touch activity is detected or if there is no UART communica-

tion. The controller automatically comes out of low power

stand by mode when a touch is detected on the touch panel

or if an incoming communication on the UART is detected. In

the low power stand by mode, all activity is disabled, includ-

ing the oscillator. Also, the LED pin is driven high. To wake

up the controller on the UART, the wake up command byte

must be sent, followed by a minimum time delay of 1ms for

the LM8500 and 3ms for the LM8300 before sending any

command byte. The delay time is needed to allow the oscil-

lator to restart and stabilize. Table 2. Startup Times shows

the average startup time for a given operating frequency.

The SHUTDOWN pin will shut down the controller when

pulled low. When the SHUTDOWN pin is pulled low, the

controller will continue to be in the low power stand by mode

until the pin is pulled high or released. While the SHUT-

DOWN pin is pulled low, all activities are stopped and any

touch or communication will be ignored. Immediately follow-

ing the SHUTDOWN pin being released or pulled high, the

controller clears the UART transmit and receive buffers and

resumes normal operation.

The controller can be put in the low power stand by mode by

sending a $A8 command to it. Upon receiving this command,

the controller goes into low power stand by mode. If the self

power down mode is enabled and the controller is put into

low power stand by mode, the controller will wake up if the

wake up command ($A7) is received or if a touch is detected

on the touch panel. If the self power down mode is disabled

and the controller is put into low power stand by mode, the

controller can only be woken up if it receives the wakeup

command. After the controller wakes up, the UART transmit

and receive buffers are cleared and resume normal opera-

tion.

TABLE 2. Startup Times

CKI Frequency Startup Time

10 MHz 1–10 ms

3.33 MHz 3–10 ms

12.0 Averaging Algorithm

To achieve better accuracy and noise filtering, each X, Y, and

Z coordinate is oversampled by specific amount. The pos-

sible oversampling settings are 1, 2, 4, 8, 16, and 32. The

factory setting is 8. The greater the oversampling, the

greater the accuracy, but the lower the CPPS.

Samples per coordinate vs. CPPS for LM8300

Samples

per coordinate

Coordinate pairs

per second (CPPS)

1 250

2 220

4 190

8 150

16 100

32 65

Samples per coordinate vs. CPPS for LM8500

Samples

per coordinate

Coordinate pairs

per second (CPPS)

1 500

2 430

4 360

8 270

16 190

32 110

12.1 DELTA ALGORITHM

The delta filter is used to remove large variations in sampled

values due to noise and glitches. The delta filter tries to

predict where the next coordinate could be. This is done by

taking the two previous coordinates and subtracting one

from the other, producing a delta value. This delta value is

then added or subtracted to the last coordinate. The result-

ing value is the predicted coordinate. If the new sampled

coordinate is close to this predicted value, then the new

value is accepted as valid and is passed to the focus algo-

rithm, provided the focus algorithm is enabled. If the new

sampled coordinate is not close to the predicted coordinate,

then the value is discarded and is stored to be used in the

following delta calculations.

The number by which the new sampled coordinate can differ

from the predicted coordinate is controlled by setting the Set

Max Delta value. The Set Max Delta value can be from a

value of 0-63. The factory default is 8.

LM8300/LM8500

www.national.com13

12.0 Averaging Algorithm (Continued)

12.2 FOCUS ALGORITHM

The focus algorithm removes some inaccuracy and noise

that could cause the coordinate to differ only by a couple of

pixels. The focus algorithm is used to eliminate the "jittering"

effect of the pointer when the pointer is stationary.

The focus algorithm compares the value of the previous

stored value to the value passed from the delta algorithm

and determines if the difference is greater than or equal to

the Set Focus Value. If the difference is greater or equal to

the value in Set Focus Value then the new coordinate is sent

out through the UART and stored as the previous value. If

the difference is less than the Set Focus Value then the

value is discarded and the stored valued is set through the

UART.

The amount of difference between the new coordinate and

the old coordinate is set in the Set Focus Value. This value

can be from 0-63 with a value of 0 disabling the focus

algorithm. The factory default is 4.

12.3 COMMUNICATION MODES

Liftoff

When set to the liftoff mode, the controller only sends data

through the UART on liftoff. The controller continuously

samples the touchscreen as long as there is a touch de-

tected on the touchscreen but only the last coordinate is sent

out to the UART.

Touchdown

When set to the touchdown mode, the controller only sends

data through the UART on touchdown. The controller con-

tinuously samples the touchscreen as long as there is a

touch detected on the touchscreen but only the first coordi-

nate is sent out to the UART.

Streaming

When set to the streaming mode, the controller continuously

sends data through the UART as long as there is a touch

detected on the touchscreen.

13.0 Brownout Reset

The device is initialized when the RESET pin is pulled low or

the On-chip Brownout Reset is activated.

The RESET input initializes the device when pulled low. The

RESET pin must be held low for a minimum of 0.5µs for the

LM8500 and a minimum of 1.5µs for the LM8300 to guaran-

tee a valid reset. Reset should also be wide enough to

ensure crystal start-up upon power-up. The R/C circuit

shown in Figure 3 is an optional circuitry that will provide a

delay 5 times (5x) greater than the power supply.

When enabled, the device generates an internal reset as

rises. While V

is less than the specified brownout

voltage (V

bor

), the device is held in the reset condition for t

= 120-128 µs for the LM8500 and t

= 360-384 µs for the

LM8300. Once the t

reaches zero, the internal reset is

released and the controller resume normal operation. This

internal reset will perform the same functions as external

reset. Once V

is above the V

bor

and t

reaches zero,

instruction execution begins. If, however, V

drops below

the selected V

bor

, an internal reset is generated, and t

is set

to 120-128 µs for the LM8500 and 360-384 µs for the

LM8300. The device now waits until V

is greater than V

bor

at which time the countdown starts over. When enabled, the

functional operation of the device, at frequency, is guaran-

teed down to the V

bor

level.

One exception to the above is that the brownout circuit will

insert a delay of approximately 3 ms on power up or any time

the V

drops below a voltage of about 1.8V. The device will

be held in Reset for the duration of this delay before t

starts

count down. This delay starts as soon as the V

rises

above the trigger voltage (approximately 1.8V). This behav-

ior is shown in Figure 4.

In Case 1, V

rises from 0V and the on-chip RESET is

undefined until the supply is greater than approximately

1.0V. At this time the brownout circuit becomes active and

holds the device in RESET. As the supply passes a level of

about 1.8V, a delay of about 3 ms (td) is started and t

preset with 120-128 µs for the LM8500 or 360-384 µs for the

LM8300. Once V

is greater than V

bor

and td has expired,

starts to count down.

Case 2 shows a subsequent dip in the supply voltage which

goes below the approximate 1.8V level. As V

drops below

bor

, the internal RESET signal is asserted. When V

rises

back above the 1.8V level, td is started. Since the power

supply rise time is longer for this case, td has expired before

rises above V

bor

and t

starts immediately when V

greater than V

bor

Case 3 shows a dip in the supply where V

drops below

bor

, but not below 1.8V. On-chip RESET is asserted when

goes below V

bor

and t

starts as soon as the supply

goes back above V

bor

20037205

FIGURE 3. Optional Reset Circuit using External Reset

LM8300/LM8500

www.national.com 14

13.0 Brownout Reset (Continued)

The internal reset will not be turned off until t

counts down

to zero. The internal reset will perform the same functions as

external reset. The device is guaranteed to operate at the

specified frequency down to the specified brownout voltage.

After the underflow, the logic is designed such that no addi-

tional internal resets occur as long as V

remains above

the brownout voltage.

The device is relatively immune to short duration negative

going V

transients (glitches). Proper filtering of the V

power supply voltage is essential for proper brownout func-

tionality. Power supply decoupling is vital even in battery

powered systems.

There are two optional brownout voltages. The part numbers

for the two versions of this device are:

LM8500, V

bor

= high voltage range.

LM8300, V

bor

= low voltage range.

Refer to the device specifications for the actual V

bor

volt-

ages.

High brownout voltage devices are guaranteed to operate at

10MHz down to the high brownout voltage. Low brownout

voltage devices are guaranteed to operate at 3.33MHz down

to the low brownout voltage. Low brownout voltage devices

are not guaranteed to operate at 10MHz down to the low

brownout voltage.

Under no circumstances should the RESET pin be allowed

to float. The RESET input may be connected to an external

pull-up resistor to V

or to other external circuitry. The

output of the brownout reset detector will always preset t

a value between 120-128µs for the LM8500 and 360-384µs

for the LM8300. At this time, the internal reset will be gener-

ated.

The device has a built in watchdog monitoring module to

prevent runaway code. To use the watchdog feature, the

WD_OUT pin must be connected to the RESET pin. The

WD_OUT pin has an internal weak pull-up so that, when the

WD_OUT pin is connected to the RESET pin, the RESET pin

does not require an external pull-up resistor to V

14.0 Calibration

The device supports two, five, and thirteen point calibration.

If desired, the calibration points can be stored internally in

the non-volatile storage element. During calibration time, the

device has the unique ability to check if the calibration points

make sense. For instance, if the desired calibration point

was to be at the upper left hand corner, but by accident, the

actual point detected was at the lower right hand corner, the

device will reject this point. This ensures the calibration

process is not performed incorrectly.

The calibration checking, can be enabled or disabled. If the

calibration checking is enabled, the controller will always

check the current calibration point being done against the

theoretical point and determine if the value is within ±127 of

the raw A/D values. If this option is desired, the touch screen

driver must perform the calibration according to the calibra-

tion mapping for the two, five, and thirteen points as shown

in Figure 5,Figure 6, and Figure 7, respectively. The theo-

retical values for the two, five, and thirteen points are shown

20037206

FIGURE 4. Brownout Reset Operation

LM8300/LM8500

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14.0 Calibration (Continued)

in Table 3. Two Points Calibration,Table 4. Five Points

Calibration, and Table 5. Thirteen Points Calibration respec-

tively.

TABLE 3. Two Points Calibration

Calibration point Theoretical X-value Theoretical Y-value

1 127 127

2 895 895

TABLE 4. Five Points Calibration

Calibration point Theoretical X-value Theoretical Y-value

1 127 127

2 895 895

3 127 895

4 511 511

5 895 127

TABLE 5. Thirteen Points Calibration

Calibration point Theoretical X-value Theoretical Y-value

1 127 127

2 895 895

3 127 895

4 511 511

5 895 127

6 895 511

7 511 895

8 127 511

9 511 127

10 623 319

11 623 623

12 319 623

13 319 319

14.1 GENERAL CALIBRATION PROCEDURES

Calibration is invoked by sending a command byte of $BD

followed by a command byte to the device. The command

byte is broken into two parts: the high nibble states the

number of calibration points to performs and the lower nibble

states the active calibration point. For example, to do the first

calibration point for the two point calibration, the command

bytes of $BD and $11 are sent to the device. The device then

echos $BD and $11 back to the TS driver and waits for a

touch on the panel. When a touch is detected, the device

checks to see if the point is within the specified parameters

if the calibration point checking is enabled. If the calibration

point checking is disabled, the device will send a $C8 for OK

byte to the TS driver regardless of where the touch was

detected. This calibration point checking can be enabled or

disabled by sending a command byte of $A5 to the device.

When all the calibration points are done, the device will do a

self-test and send a command of $CB for OK or a command

of $CC for failed. If a $CC is received, the TS driver should

issue a warning stating the calibration was not done properly

and redo the calibration procedures. The flowchart for the

calibration procedures is shown in Figure 8.

20037207

FIGURE 5. Two Points Calibration Mapping

20037208

FIGURE 6. Five Points Calibration Mapping

20037209

FIGURE 7. Thirteen Points Calibration Mapping

LM8300/LM8500

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14.0 Calibration (Continued)

14.2 CALIBRATION PROCEDURES WITH

COORDINATES CHECKING ENABLED

To do TS calibration with coordinates checking enabled, first

ensure the Calibration Coordinates Checking is enabled on

the device. This can be accomplished by sending a com-

mand byte of $B1 (Read Parameters command) and check-

ing the 5th bit of the 12th reply byte is set. Alternatively, if the

device is set to Calibration Coordinates Checking enabled

as default, this step can be skipped.

The TS driver sends the command byte to do calibration

($BD). The TS driver should wait for the reply bytes and

ensure it is the same command bytes it sent. The device

waits for a touch to be detected on the panel. Once a touch

is detected, the device checks it against the predetermined

calibration values as noted on Table 3. Two Points Calibra-

tion,Table 4. Five Points Calibration , and Table 5. Thirteen

Points Calibration. If the detected touch is within the pre-

defined value (±127 of the raw A/D value), the device will

send a command of $C4 to the TS driver and store the

calibration point in the internal flash. The TS driver can now

send a command byte to do the next calibration point. If the

detected touch is not within the predefined value, the device

will send a reply byte of $C8 to the TS driver. Upon receiving

this reply byte, the TS driver can resend the calibration

command for the same calibration point, go the next calibra-

tion point, or abort the calibration process.

Once all the calibration points are done, the device does a

self-test. If the self-test was not successful, the device will

20037210

FIGURE 8. Calibration Procedures with Coordinates Checking Enabled

LM8300/LM8500

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14.0 Calibration (Continued)

send a reply byte of $CC to the TS driver. At this point, the

TS driver should either notify the user to redo the calibration

point or automatically redo the calibration again. If the self-

test was successful, the device will send a reply byte of $CB

to the TS driver.

14.3 CALIBRATION PROCEDURES WITH

COORDINATES CHECKING DISABLED

To do TS calibration with coordinates checking disabled, first

ensure the Calibration Coordinates Checking is disabled on

the device. This can be accomplished by sending a com-

mand byte of $B1 (Read Parameters command) and check-

ing the 5th bit of the 12th reply byte is not set. Alternatively,

if the device is set to Calibration Coordinates Checking

disabled as default, this step can be skipped.

The TS driver sends the command byte to do calibration

($BD). The TS driver should wait for the reply bytes and

ensure it is the same command bytes it sent. The device

waits for a touch to be detected on the panel. Once a touch

is detected, the device save the values into the internal flash

and send a reply byte of $C4 to the TS driver. The TS driver

can now send a command byte to do the next calibration

point. Since the Calibration Checking is disabled, the TS

driver should ensure the calibration point is within the range

of the calibration cross.

Once all the calibration points are done, the device does a

self-test. If the self-test was not successful, the device will

send a reply byte of $CC to the TS driver. At this point, the

TS driver should either notify the user to redo the calibration

point or automatically redo the calibration again. If the self-

test was successful, the device will send a reply byte of $CB

to the TS driver.

15.0 Revision History

Date Section Summary of Changes

October 2002 Initial release.

May 2003 All sections Removed LM8400 part.

Brownout Reset Updated section to reflect the change and made external reset circuitry

optional.

July 2003 Advanced Command Bytes

Descriptions

Added command byte $A5

Updated controller reply bytes

December

2003

Advanced Command Bytes

Descriptions

Added description for command byte $A5

LM8300/LM8500

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16.0 Physical Dimensions inches (millimeters) unless otherwise noted

LLP Package (LQA)

Order Number LM8300HLQ9 or LM8500HLQ9

NS Package Number LQA44A

TSSOP Package (MTD)

Order Number LM8300IMT9 or LM85009IMT9

NS Package Number MTD48

LM8300/LM8500

www.national.com19

16.0 Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

Plastic Leaded Chip Carrier (VA)

Order Number LM8300HVA9 or LM8500HVA9

NS Package Number V44A

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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

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LM8300/LM8500 Four Wire Resistive Touchscreen Controller with Brownout

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.