Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 116)

Full-Duplex Protocol
Chapter 10
10Ć12
Table 10.A
Transmitter for Full-Duplex Protocol
TRANSMITTER is defined as
loop
Message=GET-MESSAGE-TO-SEND
Status=TRANSFER (Message)
SIGNAL-RESULTS (Status)
end
TRANSFER (Message) is defined as
initialize nak-limit and enq-limit
SEND (Message)
start timeout
loop
WAIT for response on path 2 or timeout.
if received DLE ACK then return SUCCESS
else if received DLE NAK then
begin
if nak-limit is exceeded then return FAILURE
else
begin
count NAK retries;
SEND-MESSAGE (message);
start timeout
end
end
else if timeout
begin
if enq-limit is exceeded then return FAILURE
else
begin
count ENQ retries;
send DLE ENQ on path 1;
start timeout
end
end
end loop
SEND (Message) is defined as
begin
BCC = O
send DLE STX on path 1
for every byte in the message do
begin
add the byte to the BCC;
send the corresponding data code on path 1
end
send DLE ETX BCC on path 1
end
GET-MESSAGE-TO-SEND
This is an operating-system-dependent interface routine that waits and allows the rest of the system to run until the message source
has supplied a message to be sent.
SIGNAL-RESULTS
This is an implementation-dependent routine that tells the message source of the results of the attempted message transfer.
WAIT
This is an operating-system-dependent routine that waits for any of several events to occur while allowing other parts of the system
to run.