GE 90-30 PLC - Manual (Page 35)

3
3-2 TCP/IP Ethernet Communications User’s Manual - August 1997 GFK-1084B
Section 1: The Communications Request
“Communications Request” 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.
H The COMMREQ Function Block (ladder instruction)
H The COMMREQ Command Block
H The Channel Command
H Status Data (COMMREQ Status word, LAN Interface Status and Channel Status
bits)
H The logic program controlling execution of the COMMREQ Function Block
The figure below illustrates the relationship of these elements:
INPUTS
AND
OUTPUTS
FOR COMMREQ
FUNCTION
COMMAND
BLOCK
POINTER
COMMREQ
FUNCTION BLOCK
DETAILS
OF THE
CHANNEL
COMMAND
COMMREQ
COMMAND BLOCK
COMMREQ
STATUS WORD
STATUS
CODES
COMMREQ
STATUS
WORD
POINTER
STATUS BITS
LAN INTERFACE STATUS
AND CHANNEL STATUS
BITS
Location in PLC memory spe-
cified when configuring the In-
terface using Configuration
Software
INITIATES
COMMREQ
FUNCTION
BLOCK
CONTROL
LOGIC
Figure 3-1. Elements of the Communications Request