Datasheet

883
32142D–06/2013
ATUC64/128/256L3/4U
CRC calculation
The CRC is calculated from the command/response, length, and data fields. The polynomial
used is the FCS16 (or CRC-16-CCIT) in reverse mode (0x8408) and the starting value is
0x0000.
Example command
Below is an example command from the master with additional data.
Figure 34-9. Example Command
Example response
Below is an example response from the slave with additional data.
Figure 34-10. Example Response
LENGTH 2
The number of bytes in the DATA
field.
Ye s
DATA LENGTH
Data according to command/
response.
Ye s
CRC 2
CRC calculated with the FCS16
polynomial.
CRC value of 0x0000 makes the aWire
disregard the CRC if the master does not
support it.
No
Table 34-30. aWire Packet Format
Field Number of bytes Description Comment Optional
baud_rate_clk
data_pin ...
field sync(0x55) command(0x81) length(MSB) length(lsb)
...
data(MSB) data(LSB) CRC(MSB) CRC(lsb)
baud_rate_clk
data_pin ...
field sync(0x55) response(0xC1) length(MSB) length(lsb)
...
data(MSB) data(LSB) CRC(MSB) CRC(lsb)