Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 63)

Asynchronous Link Protocols
Chapter 4
4-20
Examples
If a line monitor were connected to the wires between Stations A and B,
and only the A to B subsystem were active, the following would be
observed:
Normal Message
Message with Parity or BCC Error and Recovery
DLE STX ...xxx.. DLE ETX BCC
Message with ETX Destroyed
DLE STX .....xxxx [timeout] DLE ENQ
Good Message but ACK Destroyed
Messages Being Sent in Both Directions
Combined
Path 1:
DLE NAK
DLE STX .... DLE ETX BCC
DLE STX ... DLE ETX BCC
DLE STX ... DLE ETX BCC DLE STX .... DLE ETX BCC
DLE STX ...
DLE STX ... DLE ETX BCC
DLE ACK Path 2:
DLE STX .... DLE ETX BCC
DLE ACK
DLE STX .... DLE ETX BCC Path 1:
Path 2:
DLE ACK
Path 2: DLE NAK DLE ACK
Path 1:
Path 2:
Path 1:
DL xxx CK
[timeout] DLE ENQ DLE STX ... etc.
DLE ACK
Path 2:
Path 1:
Path 4:
Path 3:
DLE ACK DLE ACK
DLE ACK
DLE STX
DLE STX .... DLE ETX BCC
DLE STX ... DLE ETX BCC Circuit AB: DLE STX .... DLE ETX BCC DLE ACK DLE STX
Circuit BA: DLE STX ... DLE ACK .... DLE ETX BCC DLE ACK DLE STX
Embedded Response
ACK on AB delayed slightly because ETX BCC are indivisible.
Embedded Response Option
To simplify the design of the receiver, you can, in some cases, disable
transmission of embedded responses by turning off communication option
Switch 2 of Switch Group SW-1. If this switch is OFF, the KF2 module’s
multiplexer will not allow response codes to be sent within a message.
Instead, it will delay response codes until after it receives the next DLE
ETX BCC.