Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Uživatelský manuál stáhnout pdf (Strana 150)

Network and Application Layer Protocols

Chapter 12

123

Network Packet Fields

As we discussed the communication protocol used on the data link, we

described control characters framing the network packet. Here at the

network level, you must generate the network packet. In this protocol the

network packet characters are generated directly from binary coded bytes

of data. This provides faster throughput on the link than if this data were

coded into ASCII characters.

Figure 12.2 shows the general format of the network packet for a

command message. Figure 12.3 shows the general format of the network

packet for a reply message. Note that bytes are shown from left to right in

the order in which they are transmitted on the link.

Note that the only difference between the network packet for a command

message and the network packet for a reply message is in the high nibble

of the CMD byte.

Figure 12.2

Command

Message Packet Format

CMD STS FNC ADDR DATA

DST SRC CMD STS TNS

Data

(From Application Layer)

From

Application

Layer

10063–I

Network

Layer

Packet

1 2 ... 145 146 147 148 149 150 151 152 153 154 155 ... 238 239

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Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Uživatelský manuál Strana 150