LM8400 datasheet(18/20 Pages) NSC

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9.0 Calibration (Continued)

9.2 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 4, Table 5 , and Table 6.

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

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.

9.3 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.

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