CMC TECHNICAL REFERENCE MANUAL
1X36003 Version 2.52
1996-1999 Ingersoll-Rand Company
Date of Issue: 18-Oct-1999
109
The CMC-DF1 Interface
Introduction
Customers may want to communicate to the CMC control systems for remote compressor
control and monitoring through their Allen-Bradley data highway plus (DH+) network. Adding
Allen-Bradley DF1 protocol to the UCM module allows our customers to incorporate our
compressors into their plant-wide Allen-Bradley PLC control system. This communication
capability also provides for flexibility in the customer's compressed air operation through
remote start, stop, and data gathering for preventative maintenance.
The customer or his representative must write system software to suit his individual needs
for remote control and monitoring. Since the customer writes this interface, the system can
be as flexible as the customer desires.
One avenue for communicating with the CMC is via DF1 protocol over a full duplex RS-422
link. This requires an Allen-Bradley interface module 1770-KF2 to link our intelligent RS-
422A asynchronous device, Universal Communication Module (UCM), to the Allen-Bradley
DH+ network.
The CMC Microcontroller can communicate with other devices over a variety of
communication standards. Supported standards, or protocols, include RS-232, IRBUS
(Ingersoll-Rand Proprietary), Modicon’s MODBUS, and Allen-Bradley DF1. The built-in ports
of the CMC’s Universal Communication Module access communications. This UCM-DF1
Interface defines the message structure that a CMC Microcontroller uses to exist on a DH+
network. This interface will allow the DH+ network to gather information and control the
compressor.
The information presented in these sections that follow do not include the Allen-Bradley DF1
protocol details. Detailed information can be obtained from “Allen-Bradley Publication 1770-
6.5.117 - October 1996” -
DF1 Protocol and Command Set Reference Manual
and “
Data
Highway or Data Highway Plus Asynchronous (RS-232-C or RS-422-A) Interface Module
(Cat. No. 1770-KF2) User’s Manual
”.
A DH+ link implements peer-to-peer communication with a token-passing scheme to rotate
mastership among the nodes connected to that link. In order to communicate over Allen-
Bradley DH+ network, an Allen-Bradley 1770-KF2 interface module must be used. The
1770-KF2 always acts as one node on the DH+ network, which translates DH+ messages
to DF1 format, and passes these messages on to the UCM on the RS-422A asynchronous
end, or vice versa.
The following is a picture of 1770-KF2:
