User`s manual

GFK-1742A B-1

DSM314 Communications Request Instructions

This appendix describes two types of Communications Request (abbreviated COMM REQ in this

appendix) ladder instructions used with the DSM314:

•

Parameter Load Type:

Used to load DSM Parameter Memory. An advantage of the

COMM REQ instruction is that each one can load up to 16 parameters, and multiple COMM

REQ instructions may be used in one PLC sweep. By comparison, each Load Parameter

Immediate Command can load only one parameter per PLC sweep, with from one to four

Load Parameter Immediate commands allowed per PLC sweep, depending upon the number

of %AQ words configured (which, in turn, depends upon the number of axes configured - see

Table 5-8). Therefore, the COMM REQ is most useful for loading several or many

parameters, and the Load Parameter Immediate Command is most useful if you only need to

load a few (one to four).

•

User Data Table (UDT) Type:

Used to access the DSM314’s Local Logic User Data Table.

The User Data Table is an 8192-byte memory area that Local Logic programs can use for

data storage and retrieval. The UDT COMM REQ can copy data either from PLC word

memory to the UDT or from the UDT to PLC word memory.

In general, a COMM REQ is used in a Series 90-30 PLC ladder program to communicate with a

variety of intelligent modules. This appendix first discusses the COMM REQ instruction in

general in Sections 1 and 2, then in Sections 3 – 5, discusses how it specifically applies to the

DSM314 module. This appendix is divided into the following sections:

•

Section 1: Communications Request Overview

•

Section 2: The COMM REQ Ladder Instruction

•

Section 3: The User Data Table (UDT) COMM REQ

•

Section 4: The Parameter Load COMM REQ

•

Section 5: COMM REQ Ladder Logic Example (uses Parameter Load COMM REQ)

Appendix