Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 55)

Asynchronous Link Protocols
Chapter 4
4-12
Table 4.A
Transmitter for Full-Duplex Protocol
TRANSMITTER is defined as
loop
Message = GET-MESSAGE-TO-SEND
Status = TRANSFER (Message)
SIGNAL-RESULTS (Status)
end loop
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
if NAK-limit is exceeded then return FAILURE
else
begin
count NAK retries;
SEND-MESSAGE (Message);
start timeout
end
end
else if timeout
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 = 0
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.