Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 50)

Asynchronous Link Protocols
Chapter 4
4-7
To implement all of these data paths with only two physical circuits, a
software multiplexer combines the message codes with the response codes
going in the same direction. At the other end of the link a software
separator divides the message codes from the response codes. The
message codes are sent to the receiver, and the response codes are sent to
the transmitter via internal software. On each physical circuit, response
codes from a receiver to a transmitter will be seen intermingled with
message codes being sent from a transmitter to a receiver. Figure 4.3
shows this implementation.
Figure 4.3
Software Implementation of Data Paths
Transmitter
A
Receiver
B
S
M
M
S
Receiver
A
Transmitter
B
M S = Software Separator = Software Multiplexer
Path 2
Path 3
Path 1
Path 4
Path 2
Path 3
Path 1
Path 4
11557
Physical Circuit AB
Physical Circuit BA