Rockwell-automation 1775-KA PLC-3 Communication Adapter Module User Ma Instrukcja Użytkownika Pobierz pdf (Strona 146)

Half-Duplex Protocol

Chapter 11

1119

When a slave station’s message source and sink share a common memory

pool (as in the 1775–KA module) it may be that the message sink full

indication results from an abundance of messages in the message source,

which uses up all free pool memory. In this case, the memory can be

freed up by receiving messages from that slave station. Waiting for the

memory to clear by the action of the slave station alone may not work,

since it could be that the only way to fee up space is for the slave to send a

message to the master. This situation is illustrated in Figure 11.11.

Figure 11.11

Message

Sink Full, Case 2

Full

xxxx

SINK MASTER LINK SLAVE SINK

10061–I

DLE ACK

SOURCE/ SOURCE/

BCCDLE SOH STN

DLE STX

BCCDLE ENQ STN

Not Full

(Timeout)

DLE STX xxxx DLE ETX

BCCDLE SOH STN DLE STX xxxx DLE ETX

xxxx

Not Full

xxxx

xxxx DLE ETX BCC

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