GE GFK-1004B user manual Operation of the Communications Request

4

Operation of the Communications Request

The figure and text below explains how a Communications Request is executed. The figure specifically illustrates the operation of an Establish Read Channel Command.

Domain of a TCP connection

Domain of a channel

Client		Client
Series 90±70		Ethernet
PLC CPU	Backplane	Interface	LAN
Power flows to COMMREQ
in ladder program
Command Block sent to		Verify
Interface
		Command Block
		and set up channel
		to server PLC
		Read Request
Data		Data
		Return COMMREQ
		Status Word (CRSW)
COMMREQ		to CPU
Status Word		Pulse Data Transfer bit
Pulse received
		Read Request
Data		Data
		Pulse Data Transfer bit
Pulse received		.
.		.
		.
.
		Read Request
.
Data		Data
		Pulse Data Transfer bit
Pulse received

Server

Series 90 PLC

Data

Data

Data

Figure 4-2. Operation of the Communications Request for an Establish Read Channel-

Command

1.A Communications Request begins when there is power flow to a COMMREQ func- tion 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 Channel command, the COMMREQ Status word (CRS word) is returned immediately if the Command Block is invalid. If the syntax is correct, then the CRS word is returned after the next significant event: upon failure to establish a channel correctly and in a timely manner or upon the first successful trans- fer of data.

Once the channel is successfully set up to the server PLC, the Ethernet Interface performs the periodic reads as specified in the Command Block.

GFK-1004B Chapter 4 Programming Communications Requests 4-5