Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 121)

Full-Duplex Protocol
Chapter 10
10Ć17
begin
GET-CHAR
if char is a DLE
begin
add char to BCC
return a DLE and a data flag
end
else if char is an ACK or NAK send it to the transmitter
else if char is an ETX
begin
GET-CHAR
add char to BCC
return ETX with a control flag
end
else return character with a control flag
end
end
end
GET-CHAR is defined as
an implementation dependent function that returns one byte of data from the link interface hardware.
Full-Duplex Protocol Diagrams
The following figures show some events that can occur on the various
interfaces. Control characters are shown in bold type. Link–level data is
represented by xxxx. Line noise is represented by ???. BCC is shown at
the end of each message packet. Time is represented as increasing from
the top of the figure to the bottom. Figure 10.9 shows normal message
transfer.
Figure 10.9
Normal Message Transfer
Not Full
DLE ACK
OK
xxxx
DLE STX xxxx DLE ETX BCC
xxxx
SOURCE XMTR LINK RCVR SINK
110046–I