CRTOUCH Datasheet, PDF (25/68 Pages) Freescale Semiconductor, Inc – Capacitive and Resistive Touch Sensing Application Specific IC.

Serial Communications
3.1.6 Message format for Writing CRTouch
A write sequence comprises the transmission of the CRTouch slave address with a value of 0 for the R/W bit followed by two
bytes of information. The first byte of information is the memory map address byte and the second byte is the first data byte to
be written.
The memory map section of this document details the address of each register, its read and write permissions and the auto
increment address in case more than 1 data byte is written. Any byte received after the address byte is taken as data bytes and
is written in the location where the internal memory map logic points at that moment. A Not Acknowledge may be generated
if the location written does not exist or does not have write permissions.
Figure 21. I2C Write sequence
3.2 UART
The CRTouch device can also send and receive data through a UART communication. Default configuration is 115200 bps, 8
data bits, odd parity and one stop bit. The only configurable parameter is the baud rate through the auto-detection feature. All
the other settings are fixed.
To synchronize start and end of transactions with a host device, UART communication uses a start and end of frame reserved
characters. All the data within the data payload will be sent in unpacked BCD (that is a value of 0 x 8C will be sent in two bytes,
0 x 08 and 0 x 0C) to avoid overlapping with the start and end of frame characters.
Because there are TX and RX dedicated lines for the UART communication, for any command (read or write) there must be a
response from CRTouch, either replying to a read transaction or replying a status byte (success or error) from the previous
transaction.
3.2.1 UART Baudrate auto detection
The CRTouch comes with an auto detect feature that allows configuring any baudrate from 9600 bps to 115200 bps. To use this
feature:
1. Baudrate auto detection signal is asserted with a LOW value.
2. Host sends three consecutive bytes with 0 x 55 values with 8-data bits, odd parity, and one stop bit at the desired
baudrate to configure.
3. Finally new baudrate is configured on CRTouch.
If the requested baudrate is out of range or the values sent are not the appropriate ones to calculate a valid baudrate the last valid
value stored on the memory map is used and a Baudrate error will be indicated in the Status Error register.
CRTouch Data Sheet, Rev. 3
Freescale Semiconductor
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