LM8400 National Semiconductor, LM8400 Datasheet - Page 17

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

9.0 Calibration
9.1 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
FIGURE 8. Calibration Procedures with Coordinates Checking Enabled
(Continued)
17
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
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 $CC is received, the TS driver should
issue a warning stating the calibration was not done properly
and redo the calibration procedures. The flowchart for the
calibration procedures is shown in Figure 8.
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$
C8 for OK