9
APPENDIX B
BOILER COMMUNICATIONS MODULE (BCM)
B-1
BCM MODBUS COMMUNICATION & SUPPORT REQUIREMENTS
The Modbus communication support requirements incorporated in the BCM are as follows:
B-1.1
Function Codes
The BCM supports the Modbus Function Codes SHOWN IN Table B-1.
Table B-1. Supported Modbus Function Codes
FUNCTION CODE
03
04
06
DESCRIPTION
Read up to 8 contiguous Holding Registers
Read up to 8 contiguous Address Registers
Write a single 16 bit Register
Table B-2. Modbus Support Requirements
CHARACTERISTIC
Communication Medium
EMS Master to BCM Slave
RS 485 Alowable Cable Length
Address Support From Master EMS
Trasmission Mode Support
Timing specifications:
Baud Rate:
Data Framing:
Message Framing:
Character Framing:
Heartbeat Timeout:
DESCRIPTION
B-1.2
Modbus Support Requirements
The Modb
r
m to the suppor
us Netwo k must confor
t requirements listed in Table B-2.
RS485 2-Wire Differential Bus With Shield
4000 Feet Maximum
1 to 9 via Address Select Switch (SW1)
RTU (Remote Terminal Unit)
Fixed at 9600
8 data bits, no parity, 1 stop bit
Silent period of at least 3.5 character times Before first
character and After last character
No more than 1.5 character times of silence between
received and transmitted characters
Adjustable (0 or 1 – 240 seconds)
