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5.2.5 Feedback
A flexible function that handles all command/response functionality. One or more IOTypes are
used to perform a single write/read or multiple writes/reads.
Note that the general protocol described in Section 4.1 defines byte 2 of an extended command
as the number of data words, which is the number of words in a packet beyond the first 3 (a
word is 2 bytes). Also note that the overall size of a packet must be an even number of bytes,
so in this case an extra 0x00 is added to the end of the command and/or response if needed to
accomplish this.
Since this command has a flexible size, byte 2 will vary. For instance, if a single IOType of
PortStateRead (d26) is passed, byte 2 would be equal to 1 for the command and 3 for the
response. If a single IOType of LED (d9) is passed, an extra 0 must be added to the command
to make the packet have an even number of bytes, and byte 2 would be equal to 2. The
response would also need an extra 0 to be even, and byte 2 would be equal to 2.
Command:
Byte
0
1
2
3
4
5
6
7-63
Checksum8
0xF8
0.5 + Number of Data Words (IOTypes and Data)
0x00
Checksum16 (LSB)
Checksum16 (MSB)
Echo
IOTypes and Data
Response:
Byte
0
1
2
3
4
5
6
7
8
9-63
•
•
Checksum8
0xF8
1.5 + Number of Data Words (If Errorcode = 0)
0x00
Checksum16 (LSB)
Checksum16 (MSB)
Errorcode
ErrorFrame
Echo
Data
IOTypes & Data: One or more IOTypes can be passed in a single command, up to the
maximum packet size. More info about the available IOTypes is below. In the outgoing
command each IOType is passed and accompanied by 0 or more data bytes. In the
incoming response, only data bytes are returned without the IOTypes.
Echo: This byte is simply echoed back in the response. A host application might pass
sequential numbers to ensure the responses are in order and associated with the proper
command.
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