CRTOUCH Datasheet, PDF (26/68 Pages) Freescale Semiconductor, Inc – Capacitive and Resistive Touch Sensing Application Specific IC.

Serial Communications
3.2.2 UART communication protocol
The protocol uses the following format:
Figure 22. UART protocol format
Start of Frame — A specific byte that indicates the start of a communication between a host and CRTouch. Data byte value
0 x C0 is used for this purpose.
Register Address — Includes information if there is a write or read request from the MCU host to CRTouch, and data record
address from the CRTouch memory map. Data record address is 7-bits width, from Bit 6 to Bit 0 and write/read transaction is
located on [B7]. B7 LOW Indicates a Read transaction.
Payload Size — Information about quantity of bytes to be read or written is included on this field, this size does not include
start of frame, register address, nor end of frame.
Data bytes —Write or Read information from the the memory map. The numbers of bytes to be read or written specified in the
payload size define how many bytes each frame has. Section 4.1, “Device memory map” includes a description of the registers
address and the next address to be written or read in case of a sequential read/write operation.
End of Frame (EOF) — EOF indicates that the current communication has been finished. If the data frame transmitted from
the host MCU to the CRTouch does not include an EOF (0 x C1), the information sent from the Host to CRTouch does not have
any effect. When processing data through UART interface the command is executed upon the reception of an EOF.
Starting on the data record address byte to the last data byte to be transmitted or received by the host MCU, each data byte is
divided in MSB nibble and LSB nibble where the valid range written goes from 0 x 00 to 0 x 0F.
3.2.3 Registers Read through UART
To read any CRTouch register using the UART interface, the communication must start with a SOF followed by a register
address with the most significant bit value of ‘0’ and the amount of bytes that the host wishes to read followed by an EOF.
Upon reception of a read command, CRTouch will reply using the same UART communication protocol (SOF, Register
Address, Payload Size, Data Payload, and EOF) with the data from the registers read.
Figure 23. Register read through UART communication
CRTouch Data Sheet, Rev. 3
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Freescale Semiconductor