Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 110)

Full-Duplex Protocol
Chapter 10
10Ć6
The BCC algorithm provides a medium level of data security. It cannot
detect transposition of bytes during transmission of a packet. It also
cannot detect the insertion or deletion of data values of zero within a
packet.
Two-Way Simultaneous Operation
On a two–way simultaneous link, two physical circuits connect four
distinct and independent software routines. Figure 10.2 shows these
software routines as transmitters (XMTR) A and B and receivers (RCVR)
A and B.
Figure 10.2
Data Paths for Two-Way Simultaneous Operation
Transmitter
Receiver
B
B
A
A
Receiver
Transmitter
Path 1
Path 2
Path 3
Path 4
10039-I
There are also four independent data paths involved. Paths 1 and 3 carry
message codes between A and B; paths 2 and 4 carry response codes
between A and B.
A software multiplexer combines those message codes and response codes
going in the same direction. At the other end of the link, a software
separator separates those message codes from the response codes.
Internal software directs the message codes to the receiver and the
response codes to the transmitter. On each physical circuit, you can
intermingle response codes from a receiver to a transmitter with message
codes sent from a transmitter to a receiver (unless you do not choose the
embedded response option in LIST). Figure 10.3 shows this
implementation.