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Section 1: The Communications Request

ªCommunications Requestº is a term used to describe all the user elements required for correctly initiating Channel Commands from a Series 90 PLC. This section describes the elements of the Communications Request.

No programming of Communications Requests is required for PLCs acting as servers which are merely targets of other systems' requests but do not themselves initiate re- quests.

Structure of the Communications Request

The Communications Request is made up of the following elements.

HThe COMMREQ Function Block (ladder instruction)

HThe COMMREQ Command Block

HThe Channel Command

HStatus Data (COMMREQ Status word, LAN Interface Status and Channel Status bits)

HThe logic program controlling execution of the COMMREQ Function Block

The figure below illustrates the relationship of these elements:

CONTROL

LOGIC

INITIATES COMMREQ

COMMREQ

FUNCTION BLOCK

INPUTS

a44916c

FUNCTION

BLOCK

AND

OUTPUTS

FOR COMMREQ

FUNCTION

COMMAND

BLOCK

POINTER

COMMREQ

COMMAND BLOCK

COMMREQ

STATUS

WORD

POINTER

DETAILS

OF THE

CHANNEL

COMMAND

COMMREQ

STATUS WORD

STATUS

CODES

STATUS BITS

LAN INTERFACE STATUS AND CHANNEL STATUS BITS

Location in PLC memory spe- cified when configuring the In- terface using Logicmaster 90 Configuration Software

Figure 4-1. Elements of the Communications Request

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TCP/IP Ethernet Communications User's Manual ± January 1996

GFK-1004B

Page 90
Image 90
GE GFK-1004B user manual Structure of the Communications Request