
Publication 1794-6.5.11 - November 1997
Chapter
3
Programming Your Frequency
Input Module
What This Chapter
Contains
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, etc. 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’s 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.
To edit your ladder logic you
See page
Enter Block Transfer Instructions. . . . . . . . . . . . . . . . . . . . . . . . 3-1
PLC-2 Family Processors . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
PLC-3 Family Processors . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
PLC-5 Family Processors . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
PLC-5/250 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4