Rockwell Automation 1771-IL/B , D17716.5.91 ISOLATED ANALOG INPUT Module - Manual (Page 20)

Chapter
3
3-1
Communicating With Your Module
In this chapter, we describe
block transfer programming
quick-start sample programs in the PLC-2, PLC-3 and PLC-5
processors
module scan time issues
Your module communicates with your processor through bidirectional
block transfers. This is the sequential operation of both block transfer read
(BTR) and block transfer write (BTW) instructions.
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. The configuration BTW sets the bits which enable
the programmable features of the module, such as scaling, alarming, real
time sampling, etc. Block Transfer reads are performed to retrieve
information from the module.
Subsequent BTWs occur only when the programmer wants to write a new
configuration to the module. At all other times the module is basically in a
repetitive block transfer read (BTR) mode.
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.
The analog input module will work with a default configuration of
zeroes entered in the configuration block. This results in the default
settings of: 1 to 5V dc or 4 to 20mA (depending on voltage/current
selection jumper), BCD data format, no real time sampling (RTS), no
digital filter, no scaling, and no alarms. Refer to Chapter 4 for more
information. Also, refer to Appendix B for example configuration blocks
and instruction addresses to get started.
Your program should monitor status bits (such as overrange, underrange,
alarms, etc.) and block transfer read activity.
The following example programs illustrate the minimum programming
required for the 1771-IL series B module to powerup and operate.
Chapter Objectives
Block Transfer
Programming