Rockwell Automation 1771-N SERIES High Resolution Analog Module User Manual - Manual (Page 33)

Chapter
3
Publication 1771ĆUM127B-EN-P - December 2002
Communicating With Your
Analog Module
In this chapter, we describe
• block transfer programming
• quick-startup sample programs for the PLC-3 and PLC-5
processors
• module scan time issues
Your module communicates with the processor through bidirectional
block transfers. This is the sequential operation of both read and
write block transfer instructions.
For the 1771-N series modules, block transfer writes (BTWs) can
perform two different functions.
If you want to: Description This type of BTW is called:
configure the module
This involves settingthe bits which enable the
programmable features of the module, such as
scaling, alarming, real time sampling, etc.
the configuration BTW ”
send data to the output channels
of those modules havingoutputs
This type of BTW is generally shorter in length
than the configuring BTW because it does not
configure the module each time it is initiated.
the output update BTW"
A configuration BTW is initiated when the analog module is first
powered up, and subsequently only when the programmer wants to
enable or disable features of the module.
An output update BTW is initiated when the programmer wants the
output channels on the module to change value. This shortened
version of the BTW allows faster response time from the output
channels.
The following example programs are minimum programs; all rungs
and conditioning must be included in your application program. You
can disable BTRs, or add interlocks to prevent writes if desired. Do
not eliminate any storage bits or interlocks included in the sample
programs. If interlocks are removed, the program may not work
properly.
Chapter Objectives
Block Transfer
Programming