Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 140)

Binary Command Language
Appendix A
A-12
When the master is ready to restart communication with the scanner:
It sends a shift in character.
The scanner echoes the shift in character and resumes communication.
If the scanner does not echo the shift in character within one character
timeout period, the master device assumes that the character is not
received, and retransmits up to a maximum of three times.
After 3 unsuccessful attempts, the master sends a CCR to the scanner
and checks the protocol fault code in the CCR response. If the fault
code is:
00 hex (no fault) or 05 hex (no input buffer available), the master
should clear its error count and retransmit the last block.
Any other fault code returns, or if the scanner does not respond to
the CCR within one character timeout period, the device should
terminate communication.
Protocol Summary
Figure A.1 summarizes the protocol used with BCL. To read this diagram:
Use the: To see
left column what the processor expects to receive from your device
second column possible processor responses to your transmission
each remaining column either
• a processor response
or
• the action which the processor expects your device to
take in response to its last transmission
Important: Both the processor and the external device must respond to a
break at any time. Figure A.1 shows break conditions after each
transmission, but be aware that either the processor or the external device
stops transmitting (even in the middle of a block) when it sees a break.