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Honeywell Analytics
Introduction
Overview
The CM4 serial communications protocol was designed and developed
by Honeywell Analytics, and is proprietary information. This manual will
describe the setup and operation of the communication protocol.
Your CM4 four-point continuous monitor is equipped with an
optional serial remote device communication port. With this
communication port, you can monitor the CM4 system's operation with
equipment from a remote location. It will also allow you to gather gas
concentration data for analysis or reports.
The CM4 monitor accepts commands and issues responses to any valid
command it receives. The CM4 monitor is always considered the "slave"
device, and the remote equipment is the "master" device. The remote
equipment can be a personal computer (PC), a programmable logic
controller (PLC), or other device capable of RS-232, RS-422, or RS-485
serial communications. This configuration requires a "master" device.
Therefore, one CM4 monitor will not communicate directly with another
CM4 monitor. However, one master can be used to communicate with
more than one CM4 monitor on a two-wire RS-485 bus.
The CM4 monitor supports multiple baud rates. These user selectable
rates are 1200, 2400, 4800, 9600, and 19,200. Additional port settings
are 8-bit, 1 stop bit, and no parity.
The slave is identified by an address programmed into the CM4 monitor
(selectable 1-255). If more than one CM4 monitor is used, each must
have a unique address.
The equipment (master) is always at address 0. Each CM4 monitor will
respond to a signal directed to it from the equipment. To prevent a
collision of messages, the master must avoid transmitting any
information after a packet until the slave responds. Typically this occurs
within 1000 milliseconds.
1
CM4 Protocol Manual
Rev. 2.4 (3/05)
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