LM8400 National Semiconductor, LM8400 Datasheet - Page 10

• Manufacturer Part Number: LM8400
• Description: Four Wire Resistive Touchscreen Controller with Brownout
• Manufacturer: National Semiconductor

www.national.com
4.0 Functional Description
Set max delta
(# of pixels
from
predicted
coordinate)
Set calibration
points
Set minimum
pressure
Toggle
disable/enable
external filter
path
Toggle
disable/enable
self
power-down
Toggle
disable/enable
echo mode
Toggle
disable/enable
pressure
measurements
Toggle
disable/enable
calibration
coordinate
check
Wakeup
Shutdown
Soft reset
TSC Replies
Timeout
Re-send
Self test failed
Self test ok
Acknowledge
Calibration
coordinates
ok
Error / buffer
overrun
Software
version
Data transmit
Command
PC
$BC
$BD
$BE
$A0
$A2
$A3
$A4
$
$A7
$A8
$AF
Byte 1
A5
PC
$00-$3F
4.3.3
Advanced
Command
Bytes
Descriptions
$00-$7F
Byte 2
PC
$CA
$CA
$CA
$CA
$CA
$CA
$CA
$CA
$CA
$CA
$CF
$CE
$CC
$CB
$CA
$C4
$C8
$C7
$80/$90 Payload
Byte 1
TSC
(Continued)
$00-$3F
4.3.3
Advanced
Command
Bytes
Descriptions
$00-$7F
$00, $01
$00, $01
$00, $01
$00, $01
$00, $01
$CB, $CC
$0-$7F
(3/4 bytes)
Byte 2
TSC
10
4.3.3 Advanced Command Bytes Descriptions
Unless otherwise mentioned, all values are in hex.
$B0: Read clock-speed
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
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.
Reply Byte #1: $CA (Acknowledge)
Byte #2: Clock readout (0 = 3.3MHz, 1 = 10MHz)
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)
Byte #11: Number of calibration coordinates (0, 2, 5 or
13)
Byte #12: Toggle-flags:
1=enabled)
1=enabled)
1=enabled)
Byte #13: Pressure threshold for valid touch
Bit #5: calibration coordinates check (0=disabled,
Bit
Bit #3: Echo mode (0=disabled, 1=enabled)
Bit #2: Self Power-Down mode (0=disabled,
Bit #1: Unused
Bit #0: External filter path (0=disabled, 1=enabled)
#4:
Pressure
measurement
(0=disabled,