Rockwell-automation 1770-KF2 Data Highway or Highway Plus Interface Mo Instrukcja Użytkownika Pobierz pdf (Strona 55)

Asynchronous Link Protocols

Chapter 4

4-12

able 4.A

ransmitter 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

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 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.

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