Publication 1766-RM001A-EN-P - October 2008
Knowledgebase Quick Starts
639
How quickly a message is actually sent or received to/by a destination
device depends on a number of issues, including the selected channels
communication protocol, baud rate of the communications port, number
of retries, destination devices readiness to receive, ladder logic scan time,
etc.
Definition of the Message (MSG) instruction:
The message instruction (MSG) is an output instruction which when
configured correctly allows data to be sent or received to other
compatible devices.
The MSG instruction in the MicroLogix 1400 controller uses a Data File
MG to process the message instruction. All message elements are accessed
using the MG prefix (example: MSG done bit = MG11:0/DN).
Continuous Message Example:
The following example illustrates how, by using the MSG Done (DN) and
Error (ER) bits to unlatch the Enable (EN) bit the MSG instruction can be
configured for continuous execution.
This example uses MG11:0 for the MSG file and will require two
MicroLogix controllers one a ML1400 and the other either a ML1000 or
ML1400. The ML1400 will need to be configured as Node 1 and the other
processor as node 4.
The processor at node 1 will contain the ladder logic below and transfer
data from it's N7:0 Integer file to the processor at node 4's N7:0 Integer
file. Since N7:0 is the source file for this example, data must be entered
into this register for node 1. For this example Locate N7:0 in the ML1400
(Node 1) and enter the value 63.
TERM
A
B
COM
SHLD
CHS GND
TX
TX
PWR
TX
DC SOURCE
CABLE
EXTERNAL
MicroLogix 1400
Node 1
MicroLogix 1000
Node 4
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive