Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 129)

Appendix
A
A-1
Binary Command Language
The scanner communicates through the peripheral channel 0 on front panel
with a programming device or another external control device such as a
computer. The scanner uses the binary command language (BCL) for
communication. This chapter describes the protocol and commands of
BCL, and briefly reviews PLC-3 addressing.
BCL is a master/slave communication protocol in which the scanner is the
slave and the external device must act as the master. As slave, the scanner
cannot initiate any communications. The BCL protocol defines the rules
of communication between the scanner and an external control device. It
includes the:
method of initiating communication
format in which information must be sent to the scanner
format of scanner responses
amount of time which may elapse between commands without causing
the scanner to declare a channel timeout and stop communicating
Timeouts
BCL protocol uses four timeouts to determine if a communication problem
occurs. These timeouts guard against stopping or unnecessarily slowing
down the scanner or the master device when communication is terminated
unexpectedly (such as when a cable is detached).
If you see: It means:
Channel Timeout scanner waiting for command
Character Timeout master or scanner waiting for next character in block
Response Timeout master waiting for response block after ACK
Acknowledge Timeout master or scanner waiting for ACK
Introduction
Protocol