Tau User’s Manual Appendix B—Serial Communication Technical Details
TAU-0035-00-10, version 150 June 2011 B-11
B.4.1 Byte Count Bytes
• On all incoming and outgoing messages, the Byte-Count Bytes are used to specify
the total number of data bytes in the packet.
Note
• The Byte Count must be an even number from 0 to 0x1F4 (500 decimal).
B.4.2 CRC Bytes
• On all incoming and outgoing messages, two cyclical redundancy checks (CRCs) are
calculated using CCITT-16 initialized to 0.
• CRC1 is calculated using only the first 6 bytes of the packet.
• CRC2 is calculated using all previous bytes in the packet (i.e. bytes 0 through N).
B.5 Example of the format of a serial message
Table B-5 describes the bytes that are transferred when the FFC_MODE_SELECT (0x0B)
command is issued to the camera to set the mode to Auto (0x01) and to get the FFC mode:
The number of data bytes in the packet is not equal to the total number of bytes in the
packet. For example, a No-Op serial command contains zero data bytes.)
Table B-5: Sample FFC_MODE_SELECT (0x0B) Command
Set Message sent to camera:
Process
Code
Status Reserved Function Byte Count CRC Data CRC
0x6E 0x00 0x00 0x0B 0x00 0x02 0x0F 0x08 0x00 0x01 0x10 0x21
Response from camera to set message:
Process
Code
Status Reserved Function Byte Count CRC Data CRC
0x6E 0x00 0x00 0x0B 0x00 0x02 0x0F 0x08 0x00 0x01 0x10 0x21
Get Message sent to camera:
Process
Code
Status Reserved Function Byte Count CRC Data CRC
0x6E 0x00 0x00 0x0B 0x00 0x00 0x2F 0x4A 0x00 0x00
Response from camera to get message:
Process
Code
Status Reserved Function Byte Count CRC Data CRC
0x6E 0x00 0x00 0x0B 0x00 0x02 0x0F 0x08 0x00 0x01 0x10 0x21
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