DS41393A-Page 20

© 2009 Microchip Technology, Inc.

7.15.3.1 How the Calibration Data is Encoded and Stored in EEPROM

This section is informational only. No user action is required.

The raw touch coordinates, decoded by the controller, for each of the four calibration touches are extrapolated if

CalibrationInset

was non-zero. The four coordinate pairs are then re-oriented, if required, such that the upper left

corner is the minimum (X,Y) “origin” value pair and the lower right corner is the maximum (X,Y) value pair.

The manipulated calibration values are stored in 17 address locations of the EEPROM. In the EEPROM, the

calibration data follows the storage of the controller operating parameters. The controller operating parameters

and the calibration data are each preceded by a separator value of 0x55. Coordinates are 10-bit significant

values, scaled to 16-bit and stored in a Hi and Lo byte pair.

Separator

Upper Left (Node 1)

Upper Right (Node 2)

Lower Right (Node 3)

Lower Left (Node 4)

Flip

X

Y

X

Y

X

Y

X

Y

State

Lo

Hi

Lo

Hi

Lo

Hi

Lo

Hi

Lo

Hi

Lo

Hi

Lo

Hi

Lo

Hi

Address

0x14

0x15

0x16

0x17

0x18

0x19

0x1A

0x1B

0x1C

0x1D

0x1E

0x1F

0x20

0x21

0x22

0x23

0x24

0x25

Value

0x55

Decode the above data to as follows:

1) Swap the order of stored Lo and Hi bytes for a given coordinate.

2) Convert the 16-bit value (stored Hi and Lo bytes) from hexadecimal to decimal.

3) Divide the result by 64 to properly rescale the 16-bit stored value back to a 10-bit significant coordinate.

Example of Lo = 0x40 and Hi = 0xF3:

Swap

: 0xF340

Hex to Decimal : 62272

Divide by 64

: 973

Flip State Byte:

R = Readable bit, W = Writable bit, U = Unimplemented bit read as ‘0’

U–0

U–0

U–0

U–0

U–0

R/W

R/W

R/W

–

–

–

–

–

XYFLIP

XFLIP

YFLIP

Bit 7

Bit 0

bit 7-3 Unimplemented: Read as ‘0’

bit 2

XYFLIP:

X and Y axis flip bit

1 = X and Y axis are flipped

0 = X an Y axis are not flipped

bit 1

XFLIP:

X-axis flip bit

1 = X-axis flipped

0 = X-axis not flipped

bit 0

YFLIP:

Y-axis flip bit

1 = Y-axis flipped

0 = Y-axis not flipped