GE PACSystems RX7i, User Manual

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Chapter 7. Programming SRTP Channel Commands
112 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
Executing a Channel Command
The figure below shows how a Communications Request carries out a Channel command, in this case,
Establish Read Channel.
Client
PLC CPU Backplane
Ethernet
Interface
Server
Ethernet Interface LAN
Power flows to COMMREQ
in ladder program
Command Block sent to
Interface
Verify
Command Block
and set up channel
to server PLC
Read Request
Data
Data
Read Request
Data
Data
Client
Data
Data
COMMREQ
Status Word
Return COMMREQ
Status (CRS) Word
to CPU
.
.
.
.
.
.
Read Request
Data
Data
Data
Pulse Data Transfer bit
Data Transfer
Pulse Data Transfer bit
Pulse Data Transfer bit
Data
Domain of a channel
Domain of a TCP connection
pulse received
Data Transfer
pulse received
Data Transfer
pulse received
Domain of a remote server
Server
CPU
Backplane
Read Request
Data
Read Request
Data
Read Request
Data
PLC PLC
Figure 48: COMMREQ Sequence for Establish Read Channel
1. The command starts when there is power flow to a COMMREQ function in the client PLC. At this time,
the Command Block data is sent from the PLC CPU to the Ethernet Interface.
2. For the Establish Read Channel command, the COMMREQ status word is returned immediately if the
Command Block is invalid. If the syntax is correct, the COMMREQ status word is returned after the first
significant event: upon failure to establish a channel correctly and in a timely manner or upon the first
successful transfer of data.
3. After the channel is successfully set up to the server PLC, the Ethernet Interface performs the periodic
reads as specified in the Command Block.