Rockwell Automation 1747-KE,D17476.12 DH-485/RS-232C Interface Module - Manual (Page 121)

1 Publication 1747-UM005B-EN-P - March 2006
Appendix
B
PLC-5 to SLC 500 Communications
This appendix details how to use the PLC-5 Message instruction to
access an SLC 500 processor. This method uses PLC-2 Unprotected
Reads and Unprotected Writes to access the Common Interface File,
CIF, File 9 of an SLC processor.
Overview PLC-2 Unprotected Reads and Writes are not really implemented as
unprotected in the SLC processor. They are subject to the SLC’s file
protection schemes. For instance, they will be rejected if a download
is in process or the CIF file is already open by another device. These
types of read and write commands are somewhat universal in that
they are implemented in many other Allen-Bradley Programmable
Controllers.
• The SLC 500 and 5/01 processors use word addressing
exclusively
• The SLC 5/02, prior to Series C FRN 3 processor, also use word
addressing exclusively
• The SLC 5/02 Series B, FRN 3 processor and above have a
selection bit, S:2/8, which allows selection of either word or byte
addressing
• The DTAM for the SLC processors use word addressing
exclusively
The CIF is actually like any of the other SLC data files except that it is
designated as the target file for all PLC-2 Unprotected Read and
Unprotected Write commands that are received by the SLC. It is
always File 9. The CIF can be defined as bit, integer, timer, counter, or
control data types. However, only bit or integer files should be used to
make addressing easier.
IMPORTANT
Although the format of the Unprotected Reads and
Writes is the same as used in other PLC processors,
the implementation of the address parameter is
different. In Allen-Bradley’s PLC products, the
address is interpreted as a byte address. In some SLC
500 products, the address is interpreted as a word
address.