GE PACSystems RX7i, User Manual

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GFK-2224Q January 2017 94
Chapter 6
Programming EGD Commands
This chapter describes a set of commands that can be used in the application program to read and write data
over the Ethernet network:
▪
Read PLC Memory
▪
Write PLC Memory
▪
Read EGD Exchange
▪
Write EGD Exchange
▪
Masked Write to EGD Exchange
6.1 General Use of EGD Commands
COMMREQ-driven EGD Commands can be used in the application program to read and write data into
PACSystems PLCs or other EGD Class 2 devices.
The Ethernet interface supports a maximum of 10 simultaneous EGD commands.
6.2
Using EGD Commands in a Redundancy System
When two Ethernet Interfaces are configured for Redundant IP operation (see Chapter 1,
“Introduction”
, for
more information), only the active unit sends or responds to EGD commands. The backup unit does not send or
respond to the Redundant IP address. If the backup unit tries to send an EGD command, a COMMREQ error
status is returned to its application program.
If the active Ethernet interface changes to backup status, it takes down all reliable datagram services (RDS)
sessions that use the Redundant IP address. Any EGD command currently in process over the Redundant IP
address when a role switch occurs is ended.
Although not recommend, EGD commands may be issued to the direct IP address. Both the active and backup
units will respond to EGD commands received at the direct IP address. (Remote hosts should use the
Redundant IP address when communicating to a redundant system.)
6.3
COMMREQ Format for Programming EGD Commands
The EGD commands described in this chapter are sent using the Communications Request (COMMREQ)
function.
The Communications Request is triggered when the logic program passes power to the COMMREQ Function
Block.
(Enable )
-------------
(Command Block address)
(Rack/Slot Location of
the Ethernet Interface)
(Task value)
-
-
-
-
Function Faulted (logic)
COMM
REQ
IN FT
SYSID
TASK
-
CommReq Delivered
Figure 46: COMMREQ Used to Program Ethernet Global Data
For the EGD commands, the parameters of the COMMREQ are: