3M SC400 Serial Resistive, Reference Manual

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SC400 Controller Communications 21
3M Touch Systems Proprietary Information
Format Tablet
Syntax: <SOH> FT <CR>
Response: <SOH> 0 <CR> Positive response.
The controller will respond with ACK for compatibility with older controllers. This
format is the only format supported by this controller.
With the controller in Format Tablet mode, touching the screen causes the controller to
return a response in the following format:
SXxYy
S = Status byte, first byte of data. Refer to Table 4.
Xx = X (horizontal) coordinate data; second and third bytes of data.
Yy = Y (vertical) coordinate data; fourth and fifth bytes of data.
Description: Outputs the X/Y touch coordinate data in a 5-byte packet. The packet includes 1 status
byte and 4 bytes of binary X/Y coordinate data. The protocol also establishes the X and Y
coordinate output as 14 binary bits providing a range of 0 to 16,383.
The low order bits (X3 – X0 and Y3 – Y0) are not significant in a 1024 by 1024 touch
screen because data can fluctuate with each touch, and therefore may not be completely
accurate.
Table 4 Data Sequence
Most Significant Bit
Bits
Least Significant Bit
Data Sequence 7 6 5 4 3 2 1 0
S Byte 1 1 S6 S5 S4 S3 S2 S1 S0
X Byte 2 0 X6 X5 X4 X3 X2 X1 X0
X Byte 3 0 X13 X12 X11 X10 X9 X8 X7
Y Byte 4 0 Y6 Y5 Y4 Y3 Y2 Y1 Y0
Y Byte 5 0 Y13 Y12 Y11 Y10 Y9 Y8 Y7
Table 5 defines the status bits (Byte 1) for the Format Tablet data.
Table 5 Format Tablet Status Bits
Bit Description Values
S0 – S5 Reserved —
S6 Proximity (touch state) 1 = Touch screen is being touched (a touchdown or a continued touch).
0 = Touch screen is not being touched (a touch liftoff or inactive).
When the proximity bit changes from 1 to 0 (touch liftoff), the controller
outputs one final set of X/Y coordinate data with the bit equal to 0 and the
X/Y coordinate data equal to the last touch point.
S7 Packet synchronization Always 1.