Rockwell Automation 1794-IJ2XT FLEX I/O Frequency Input Modules User Manual - Manual (Page 75)

65 Publication 1794-6.5.11 - September 2011
Appendix
D
Program Your Module with PLC Processors
Overview This Appendix serves as a reference to users of the PLC-* Family Processors
to program their modules.
To initiate communication between the frequency input module and your PLC
processor, you must enter block transfer instructions into your ladder logic
program. Use this chapter to enter the necessary block transfer instructions
into your ladder logic program.
Enter Block Transfer
Instructions The frequency input module communicates with the PLC processor through
bidirectional block transfers. This is the sequential operation of both read and
write block transfer instructions.
Before you configure the module, you need to enter block transfer instructions
into your ladder logic. The following example programs illustrate the minimum
programming required for communication to take place between the module
and a PLC processor. These programs can be modified to suit your application
requirements.
A configuration block transfer write (BTW) is initiated when the frequency
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 scalars
and alarm values, and so on. Block transfer reads are performed to retrieve
information from the module.
Block transfer read (BTR) programming moves status and data from the
module to the processor data table. The processor user program initiates the
request to transfer data from the module to the processor. The transferred
words contain module status, channel status and input data from the module.
Your program should monitor status bits, block transfer read and block
transfer write activity.