Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Manual de usuario descargar pdf (Pagina 108)

Full-Duplex Protocol

Chapter 10

104

DLE ACK – signals that the receiver has successfully received the last

message sent.

DLE NAK – signals that the receiver did not successfully receive the

last message sent.

Link-Layer Message Packets

A link–layer message packet starts with a DLE STX, ends with a DLE

ETX BCC, and includes all link–layer data codes in between. Data codes

can occur only inside a message packet.

Response codes occur inside a message packet. If you select the

embedded responses option with LIST (chapter 2) the response codes can

also occur between a DLE STX and a DLE ETX BCC, but these response

codes are not part of the message packet: they are referred to as embedded

responses.

Figure 10.1 shows the format of a link–layer message packet for

full–duplex protocol, and the layer at which each portion should be

implemented. At the end of each message packet is the one–byte BCC

field.

Figure 10.1

Link

Packet Format for Full-Duplex Protocol

10038-I

CMD STS

FNC

ADDR

DATA

DLE

STX

Data

DLE

ETX

BCC

(From Network Layer)

DST SRC CMD STS TNS

Data

(From Application Layer)

–––––––––– –––

––––––––––

From

Applicaion

Layer

From

Network

Layer

1 2 ... 103 104 105 106 107 108 109 110 111 112 113 ... 238 239

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Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Manual de usuario Pagina 108

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