User`s guide

Page 16

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

4. 1746-C General Theory of Operation

4.1. Operational Overview

The interface for the PLC with the actuators (through the 1746-C module) is with an array of 25 tables

… 64 words per table with the table number (command) in Word # [0] of each. This is based on the

M0/M1 interface protocol established by Allen-Bradley for the SLC-500 systems.

The 1746-C operates using a “Non-Interruptible Time-Slice Process Allocation

” communication

methodology. This means that it must finish executing the process that is executing in its allocated

time-slice before another process can operate. The two processes being scheduled are:

• Scanning the network for data.

• Interfacing with the PLC.

This means that the 1746-C will ignore any new commands from the PLC while scanning the network

(during the network scan time-slice) and no network scanning will take place while processing a

command from the PLC (during the PLC interface time-slice).

4.1.1. Diagram Describing Relationship Between Process Time Slices

Process time slicing is how the 1746-C divides its time when performing its 2 primary communication

tasks … communicating with the PLC and communicating with the actuator network.

This diagram helps demonstrate the relationship between the two communication processes.

PLC

PLC Backplane

1746-C

1746-C Actuators on

Network Communications

(Network Scan Time Slice)

PLC  1746-C

Communications

(PLC Interface Time Slice)