Executing A Channel Command - GE RX3i User Manual

Chapter 7. Programming SRTP Channel Commands

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
Power flows to COMMREQ
in ladder program
Command Block sent to
Interface
Data
COMMREQ
Status Word
Data Transfer
pulse received
Data
Data Transfer
pulse received
.
.
.
Data
Data Transfer
pulse received
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.
112 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual
Domain of a channel
Client
PLC Ethernet
Backplane Interface
Verify
Command Block
and set up channel
to server PLC
Read Request
Data Data
Return COMMREQ
Status (CRS) Word
to CPU
Pulse Data Transfer bit
Read Request
Data
Pulse Data Transfer bit
.
.
.
Read Request
Data
Pulse Data Transfer bit
Figure 48: COMMREQ Sequence for Establish Read Channel
Domain of a TCP connection
Server
LAN
Ethernet Interface
Read Request
Data
Read Request
Data
Read Request
Data
Domain of a remote server
PLC
Server
Backplane
CPU
Data
Data
Data
GFK-2224Q