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