Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 146)

Half-Duplex Protocol
Chapter 11
11Ć19
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
OK
xxxx
xxxx
SINK MASTER LINK SLAVE SINK
10061–I
DLE ACK
SOURCE/ SOURCE/
BCC DLE SOH STN
DLE STX
BCC DLE ENQ STN
Not Full
(Timeout)
DLE STX xxxx DLE ETX
BCC DLE SOH STN DLE STX xxxx DLE ETX
xxxx
Not Full
xxxx
xxxx DLE ETX BCC