User`s guide

Page 24

Controlinc 1746-C (Version 5.21) Network Master Users Guide (2004-11-18)

4.3. PLC Interface Time-Slice (1746-C

↔

PLC Communication)

The primary interface for the PLC with the 1746-C module is with an array of 25 tables (labeled 0  24)

stored in the 1746-C RAM. Each table is 64-words long and each word is 16-bits. From the

perspective of the PLC interfacing with the network, some of the tables are “read only” and some are

“read/write” (depending upon a command word).

Relative to M0/M1 transfers, from the 1746-C perspective, there is no difference in handling “table

reads” or “table writes” … they both require a M0/M1 file transfer command.

The Relay Ladder Logic (RLL) in the PLC CPU interfaces with the 1746-C module with the M0/M1 file

transfer mechanism and transferring fixed blocks of 64 words (a table) with the table number

(command) in Word # [0] of each transfer.

• To send a table to the 1746-C (either as a write table command or to indicate a particular table

to read back), the PLC must send the desired table in the data portion of the M0 file.

• To read back a table, the PLC must read the M1 file sent from the 1746-C.

Note: Since the 1746-C must be mounted in the local chassis (in the same chassis as the CPU), the

RLL cannot use the BTR/BTW block transfer command set (BTR/BTW commands cannot be

used over the back plane in the SLC systems). Therefore, the RLL must implement the

transfer using the “copy file” command … copying the M0/M1 files back and forth.

Note: Refer to the following Allen Bradley Documents:

• Allen Bradley SLC-500 Instruction Set Reference,

Publication 1747-RM001D-EN-P (November-2003)

• Allen-Bradley SLC-500 BASIC User's Manual (1746-BAS & 1746-BAS-T)

Publication No. 1746-UM004A-US-P 2000