Rockwell Automation 1771-IFE , D17716.5.90 USER MNL. ANALOG INPUT Module - Manual (Page 25)

Chapter
3
3-1
Module Programming
In this chapter we describe:
block transfer programming
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 read and write
block transfer instructions.
The block transfer write (BTW) instruction is initiated when the analog
module is first powered up, and subsequently 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 application programs for the three processor families were written to
accomplish this handshaking in the described manner. They are minimum
programs; all the rungs and conditioning must be included in your
application program. If you wish to disable BTRs for any reason, or add
interlocks to the BTW rung to prevent writes from happening at certain
times, you are allowed to do it. You may not eliminate any storage bits or
interlocks that are included in our examples. If interlocks are removed, the
program may not work properly.
The analog input module will work with a default configuration of
zeroes entered in all five words of a five word BTW configuration
block. See the configuration default section to understand what this
configuration will look like. Also, refer to Appendix B for example
configuration blocks and instruction addresses to get started.
ATTENTION: In PLC-2 family processors you must not
enable both the read and write instructions at the same time.
Undesirable data could transfer, resulting in unpredictable
machine operation. Using the prescribed programs will prevent
this situation.
Chapter Objectives
Block Transfer
Programming