Rockwell Automation 1771-IJ_IK IK ENCODER/COUNTER MODULES - Manual (Page 27)

Chapter
4
Publication 1771ĆUM006B-EN-P - June 2002
Module/Processor
Communication
Communication between the processor and the encoder/counter
module is bidirectional. This means that information is transferred
to and from the module: the processor instructs the module to
perform specific functions and may provide values to be compared
on the module and used for output control; the module transmits its
accumulated count and other status information to the processor.
Because both input and output data are transmitted between this
module and the processor, special programming techniques are used
to coordinate and control this bidirectional data transfer.
Complete 16–bit words are transferred between the module and the
processor. The processor sends up to 3 words of data to the
encoder/counter module:
Control word
Preset word #1
Preset word #2
These are termed the output words since they are output with respect
to the program.
The encoder/counter module sends a status word to the processor.
Figure 4.1 shows the transfer of output and input words in
bidirectional module/processor communication, described in the
following paragraphs.
Figure 4.1
Bidirectional Module/Processor Communication
15950
Encoder/Counter Module, Cat. No. 1771ĆIJ/IK
Output Words
Input Words
Optional
Status Word
Control Word
Preset Word #1
Preset Word #2
General