NSC LM8500IMT9 Four wire resistive touchscreen controller with brownout Datasheet

December 2003
LM8300/LM8500
Four Wire Resistive Touchscreen Controller with
Brownout
1.0 General Description
The LM8300/8500 is a 4-wire resistive touch screen controller. 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 SHUTDOWN 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
5V
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
n Supports 4 wire resistive touch panels
n Low power standby current typically less than 2 µA at
5.5V
n Maximum speed of 500 coordinate pairs per second
n Automatic wake up and return to standby
n 10 bit A/D
n On-chip touch screen current drivers - no external driver
required
n UART interface
n Controller configurations are stored in the internal
non-volatile storage element
n Touch pressure can be measured
APPLICATIONS
n Personal Digital Assistants
n Smart Hand-Held Devices
n Touch Screen Monitors
n Point-of-Sales Terminals
n KIOSK
n Pagers
n Cell Phones
COP8™ is a trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation
DS200372
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LM8300/LM8500 Four Wire Resistive Touchscreen Controller with Brownout
PRELIMINARY
LM8300/LM8500
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
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H = 44 Pin
I = 48 Pin
2
LQ = LLP
MT = TSSOP
VA = PLCC
9 = 0 to +70˚C
3
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LM8300/LM8500
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
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
20037204
* This pin is available in the LM8500. It is unused in the LM8300.
Top View
TSSOP Package
See NS Package Number MTD48
20037203
* This pin is available in the LM8500. It is unused in the LM8300.
Top View
LLP Package
See NS Package Number LQA44A
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4
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
O
Watchdog output, tie to RESET pin
for correct function
8
3
3
I
Used to set if crystal is 3.3 MHz (low)
or 10 MHz (floating or pulled high)
9
4
4
WD_OUT
CLK_SET1
Unused2
10
5
5
Unused2
11
6
6
Unused2
12
7
7
Unused
2
13
8
8
OSC_OUT
O
Clock oscillator output
14
9
9
OSC_IN
I
Clock oscillator input
15
10
10
2
16
11
11
Unused2
17
12
12
Unused
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
Unused2
21
16
16
Unused2
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
Unused2
28
23
23
Unused2
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
AVCC
Analog power supply, connect to filter
for best performance
34
29
31
VCC
Digital power supply
35
30
32
X
X
33
Unused2
Unused
2
X
X
34
Unused2
36
31
35
Unused2
37
32
36
2
38
33
37
Unused2
39
34
38
Unused2
40
35
39
Unused2
41
36
40
Unused
5
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LM8300/LM8500
6.0 Pin Descriptions
LM8300/LM8500
6.0 Pin Descriptions
(Continued)
Pinouts for 44- and 48-Pin Packages (Continued)
Pin Name
LED
Direction
Pin Description
Optional LED output, low when
running, high in halt-mode
44-Pin LLP
44-Pin PLCC 48-Pin TSSOP
42
37
41
Unused2
3
42
46
2
4
43
47
Unused2
5
44
48
Unused
Output
Note 1: This is available in the LM8500 only.
Note 2: These pins are for future functional expansions.
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6
Total Current out of GND Pin (Sink)
3)
Storage Temperature Range
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Protection Level
Supply Voltage (VCC)
Voltage at Any Pin
−65˚C to +140˚C
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.
7V
−0.3V to VCC +0.3V
Total Current into VCC Pin (Source)
200 mA
200 mA
8.0 Electrical Characteristics
DC Electrical Characteristics (0˚C ≤ TA ≤ +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 106
ns
0.1 VCC
V
Power Supply Ripple (Note 4)
Peak-to-Peak
Supply Current (Note 5)
High Speed Mode
CKI = 10 MHz
VCC = 5.5V
11.5
mA
CKI = 3.33 MHz
VCC = 4.5V
5
mA
10
µA
45
µA
HALT Current with BOR Disabled (Note 6)
High Speed Mode
Supply Current for BOR Feature
<2
VCC = 5.5V, CKI = 0 MHz
VCC = 5.5V
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 (VIH, VIL)
Logic High
0.8 VCC
V
Logic Low
Internal Bias Resistor for the CKI
Crystal/Resonator Oscillator
0.16 VCC
V
2.5
MΩ
−0.5
+0.5
µA
−50
−210
µA
0.3
Hi-Z Input Leakage
VCC = 5.5V
Input Pullup Current
VCC = 5.5V, VIN = 0V
Port Input Hysteresis
1.0
0.25 VCC
V
Output Current Levels
Outputs X+, X-, Y+, YSource (Note 7)
VCC = 4.5V, VOH = 4.2V
−10
mA
VCC = 2.7V, VOH = 2.4V
−6
mA
Sink (Note 7)
VCC = 4.5V, VOL = 0.3V
10
mA
VCC = 2.7V, VOL = 0.3V
6
mA
Allowable Sink and Source Current per Pin
20
mA
All Others
Source (Weak Pull-Up Mode)
VCC = 4.5V, VOH = 3.8V
−10
VCC = 2.7V, VOH = 1.8V
−5
µA
Source (Push-Pull Mode)
VCC = 4.5V, VOH = 3.8V
−7
mA
VCC = 2.7V, VOH = 1.8V
−4
mA
Sink (Push-Pull Mode) (Note 7)
VCC = 4.5V, VOL = 1.0V
10
mA
VCC = 2.7V, VOL = 0.4V
3.5
Allowable Sink and Source Current per Pin
TRI-STATE Leakage
VCC = 5.5V
−0.5
Maximum Input Current without Latchup
RAM Retention Voltage, VR (in HALT Mode)
2.0
7
µA
mA
15
mA
+0.5
µA
± 200
mA
V
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LM8300/LM8500
7.0 Absolute Maximum Ratings (Note
LM8300/LM8500
8.0 Electrical Characteristics
(Continued)
DC Electrical Characteristics (0˚C ≤ TA ≤ +70˚C)
(Continued)
Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Parameter
Conditions
Min
Typ
Input Capacitance
Note 4: Maximum rate of voltage change must be < 0.5 V/ms.
Max
Units
7
pF
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 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 7: Absolute Maximum Ratings should not be exceeded.
A/D Converter Electrical Characteristics (0˚C ≤ TA ≤ +70˚C) (Single-ended
mode only)
Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Parameter
Conditions
Min
Typ
Resolution
DNL
VCC = 5V
DNL
VCC = 3V
INL
VCC = 5V
INL
VCC = 3V
Offset Error
VCC = 5V
Offset Error
VCC = 3V
Gain Error
VCC = 5V
Gain Error
VCC = 3V
Input Voltage Range
2.7V ≤ VCC < 5.5V
Units
10
Bits
±1
±1
±2
±4
± 1.5
± 2.5
± 1.5
± 2.5
LSB
LSB
LSB
LSB
LSB
LSB
LSB
LSB
VCC
V
Analog Input Leakage Current
0.5
µA
Analog Input Resistance (Note 8)
6k
Ω
Analog Input Capacitance
7
pF
0.6
mA
Operating Current on AVCC
0
Max
AVCC = 5.5V
0.2
Note 8: Resistance between the device input and the internal sample and hold capacitance.
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 frequency 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.
9.0 Functional Description
9.1 GENERAL
The LM8300/8500 is a 4-wire resistive touch screen controller. 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 nonvolatile 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: oversampling, 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 algorithms 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.
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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.
8
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.
(Continued)
LED — Optional LED output. When the controller is operating 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.
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).
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
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
X2
X1
X0
Y2
Y1
Y0
GND — Digital Ground
Byte 3
0
X9
X8
X7
X6
X5
X4
X3
AGND — Analog ground
DVCC — Digital power supply.
AVCC — 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:
Byte 4
0
Y9
Y8
Y7
Y6
Y5
Y4
Y3
Byte 5
0
Z6
Z5
Z4
Z3
Z2
Z1
Z0
L - Package length. (0 = 4 bytes, 1 = 5 bytes)
S - Touch state (0 = liftoff, 1 = touchdown or continuous
touch)
XX - X position (10 bit value)
YY - Y position (10 bit value)
ZZ - Z positon (7 bit value), this byte is only transmitted if the
pressure measurement is enabled
9.3.2 Command Bytes
PC
Command
20037216
PC
Byte
1
PC
Byte 2
TSC
Byte 1
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
FIGURE 1. LLP Package Bottom View
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 command 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).
9
TSC
Byte 2
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LM8300/LM8500
9.0 Functional Description
LM8300/LM8500
9.0 Functional Description
PC
Command
Read stored
calibration
points
Set focus
value (# of
pixels on
touch panel)
PC
Byte
1
PC
Byte 2
$B4
$B8
TSC
Byte 1
$CA
$0-$3F
$CA
(Continued)
TSC
Byte 2
$00-$3F
$01, $02,
$04, $08,
$10, $20
Set
$BB
communication
mode
(stream,
touchdown,
liftoff)
$01, $02,
$04
Set max delta $BC
(# of pixels
from
predicted
coordinate)
$00-$3F
Set calibration $BD
points
Section
$CA
9.3.3
Advanced
Command
Bytes
Descriptions
Section
9.3.3
Advanced
Command
Bytes
Descriptions
$00-$7F
$CA
$00-$7F
Toggle
$A0
disable/enable
external filter
path
$CA
$00, $01
Toggle
$A2
disable/enable
self
power-down
$CA
$00, $01
Toggle
$A3
disable/enable
echo mode
$CA
$00, $01
Toggle
$A4
disable/enable
pressure
measurements
$CA
$00, $01
Set minimum
pressure
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$BE
$CA
$CA
PC
Byte
1
PC
Byte 2
Toggle
$A5
disable/enable
calibration
coordinate
check
Section
9.3.3
Advanced
Command
Bytes
Descriptions
Set # of
$BA
samples per
coordinate (1,
2, 4, 8, 16,
32)
$CA
PC
Command
TSC
Byte 1
$CA
Wakeup
$A7
Shutdown
$A8
$CA
Soft reset
$AF
$CA
TSC
Byte 2
$00, $01
$CB, $CC
TSC Replies
$01, $02,
$04, $08,
$10, $20
$01, $02,
$04
Timeout
$CF
Re-send
$CE
Self test failed
$CC
Self test ok
$CB
Acknowledge
$CA
Calibration
coordinates
ok
$C4
Error / buffer
overrun
$C8
Software
version
$C7
Data transmit
$80/$90 Payload (3/4
bytes)
$00-$3F
$0-$7F
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 determines 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)
10
- 4 samples/coordinate, $08 - 8 samples/coordinate,
$10 - 16 samples/coordinate, $20 - 32
samples/coordinate)
(Continued)
Byte #11: Number of calibration coordinates (0, 2, 5 or
13)
Byte #12: Toggle-flags:
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)
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)
This command allows the selection of different sample numbers 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
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
Byte #2: Communication mode ($01 = stream, $02 =
touchdown, $04 = liftoff)
Reply Byte #1: $CA (Acknowledge)
This command allows the user to read all the selected parameters. 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: 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)
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)
See the averaging algorithms section for a detailed description 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)
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)
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)
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 identical 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
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 external 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
11
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LM8300/LM8500
9.0 Functional Description
LM8300/LM8500
9.0 Functional Description
CONTROLLER REPLIES
$CF: Timeout.
(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
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)
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
$CA: Acknowledge
$C4: Calibration coordinates OK
This is sent if the coordinates are within the predefined
value.
$C8: Error / TX Buffer overrun
Reply Byte #1: $CA (Acknowledge)
Byte #2: (0 = now disabled, 1 = now enabled)
The echo mode is available for debugging purposes. If enabled, 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)
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: (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)
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.)
If the cablibration checking is enabled, the cablibration mapping must be the values shown in ??? to ???.
$A7: Wakeup
Byte
Byte
Byte
Byte
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)
Status, low X and low Y
High X
High Y
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,
TA = 25˚C, VCC = 5V shows the component values required
for various standard crystal values. Figure 2 shows the
crystal oscillator connection diagram.
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 command. If the self-power-down mode is disabled, then only the
wakeup command can wake-up the controller from shutdown 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)
20037215
FIGURE 2. Crystal Oscillator
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.
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#2:
#3:
#4:
#5:
12
command. After the controller wakes up, the UART transmit
and receive buffers are cleared and resume normal operation.
(Continued)
TABLE 1. Crystal Oscillator Configuration,
TA = 25˚C, VCC = 5V
TABLE 2. Startup Times
C1 (pF)
C2 (pF)
CKI Freq.
(MHz)
CKI Frequency
Startup Time
18
18
10
10 MHz
1–10 ms
18–36
18–36
3.27
3.33 MHz
3–10 ms
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.
12.0 Averaging Algorithm
To achieve better accuracy and noise filtering, each X, Y, and
Z coordinate is oversampled by specific amount. The possible 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.
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 = (C1 * C2) / (C1 + C2) +
Cparasitic
C2 can be trimmed to obtain the desired frequency. C2
should be less than or equal to C1.
Samples per coordinate vs. CPPS for LM8300
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 controller automatically goes into low power stand by if no more
touch activity is detected or if there is no UART communication. 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, including 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 oscillator 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 SHUTDOWN pin is pulled low, all activities are stopped and any
touch or communication will be ignored. Immediately following 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
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 resulting 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 algorithm, 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.
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LM8300/LM8500
10.0 Oscillator
LM8300/LM8500
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.
20037205
FIGURE 3. Optional Reset Circuit using External Reset
When enabled, the device generates an internal reset as
VCC rises. While VCC is less than the specified brownout
voltage (Vbor), the device is held in the reset condition for tid
= 120-128 µs for the LM8500 and tid = 360-384 µs for the
LM8300. Once the tid 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 VCC is above the Vbor and tid reaches zero,
instruction execution begins. If, however, VCC drops below
the selected Vbor, an internal reset is generated, and tid is set
to 120-128 µs for the LM8500 and 360-384 µs for the
LM8300. The device now waits until VCC is greater than Vbor,
at which time the countdown starts over. When enabled, the
functional operation of the device, at frequency, is guaranteed down to the Vbor 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 VCC drops below a voltage of about 1.8V. The device will
be held in Reset for the duration of this delay before tid starts
count down. This delay starts as soon as the VCC rises
above the trigger voltage (approximately 1.8V). This behavior is shown in Figure 4.
In Case 1, VCC 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 tid is
preset with 120-128 µs for the LM8500 or 360-384 µs for the
LM8300. Once VCC is greater than Vbor and td has expired,
tid starts to count down.
Case 2 shows a subsequent dip in the supply voltage which
goes below the approximate 1.8V level. As VCC drops below
Vbor, the internal RESET signal is asserted. When VCC 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
VCC rises above Vbor and tidstarts immediately when VCC is
greater than Vbor.
Case 3 shows a dip in the supply where VCC drops below
Vbor, but not below 1.8V. On-chip RESET is asserted when
VCC goes below Vbor and tid starts as soon as the supply
goes back above Vbor.
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 detected 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 continuously samples the touchscreen as long as there is a
touch detected on the touchscreen but only the first coordinate 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 guarantee 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.
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14
LM8300/LM8500
13.0 Brownout Reset
(Continued)
20037206
FIGURE 4. Brownout Reset Operation
a value between 120-128µs for the LM8500 and 360-384µs
for the LM8300. At this time, the internal reset will be generated.
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 VCC.
The internal reset will not be turned off until tid 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 additional internal resets occur as long as VCC remains above
the brownout voltage.
The device is relatively immune to short duration negative
going VCC transients (glitches). Proper filtering of the VCC
power supply voltage is essential for proper brownout functionality. 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, Vbor = high voltage range.
LM8300, Vbor = low voltage range.
Refer to the device specifications for the actual Vbor voltages.
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 VCC or to other external circuitry. The
output of the brownout reset detector will always preset tid to
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 calibration mapping for the two, five, and thirteen points as shown
in Figure 5, Figure 6, and Figure 7, respectively. The theoretical values for the two, five, and thirteen points are shown
15
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LM8300/LM8500
14.0 Calibration
TABLE 3. Two Points Calibration
(Continued)
Calibration point Theoretical X-value Theoretical Y-value
in Table 3. Two Points Calibration, Table 4. Five Points
Calibration, and Table 5. Thirteen Points Calibration respectively.
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
20037207
FIGURE 5. Two Points Calibration Mapping
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.
20037208
FIGURE 6. Five Points Calibration Mapping
20037209
FIGURE 7. Thirteen Points Calibration Mapping
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1
16
LM8300/LM8500
14.0 Calibration
(Continued)
20037210
FIGURE 8. Calibration Procedures with Coordinates Checking Enabled
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 command byte of $B1 (Read Parameters command) and checking the 5th bit of the 12th reply byte is set. Alternatively, if the
device is set to Calibration Coordinates Checking enabled
as default, this step can be skipped.
The TS driver sends the command byte to do calibration
($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 Calibration, Table 4. Five Points Calibration , and Table 5. Thirteen
Points Calibration. If the detected touch is within the predefined 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 calibration 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
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LM8300/LM8500
14.0 Calibration
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 selftest was successful, the device will send a reply byte of $CB
to the TS driver.
(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 selftest 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 command byte of $B1 (Read Parameters command) and checking the 5th bit of the 12th reply byte is not set. Alternatively,
if the device is set to Calibration Coordinates Checking
disabled as default, this step can be skipped.
The TS driver sends the command byte to do calibration
($BD). The TS driver should wait for the reply bytes and
15.0 Revision History
Date
Section
October 2002
May 2003
July 2003
December
2003
www.national.com
Summary of Changes
Initial release.
All sections
Removed LM8400 part.
Brownout Reset
Updated section to reflect the change and made external reset circuitry
optional.
Advanced Command Bytes
Descriptions
Added command byte $A5
Advanced Command Bytes
Descriptions
Added description for command byte $A5
Updated controller reply bytes
18
LM8300/LM8500
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
19
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LM8300/LM8500 Four Wire Resistive Touchscreen Controller with Brownout
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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