LM8300 datasheet(17/20 Pages) NSC

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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 Datasheet(PDF) 17 Page - National Semiconductor (TI)