GF-135
Esteem 399 Low NOx Boiler
Chapter 18
OMM-0089_0A
Installation, Operation & Maintenance Manual Controller Operation
Page
169
of
188
AERCO International, Inc.
•
100 Oritani Dr.
•
Blauvelt, NY 10913
OMM-0089_0A
MC1 06/19/14
Ph.: 800-526-0288
18.9.15 Modbus Interface
The Modbus Interface allows a Building Management System (BMS) to directly connect to the
boiler. A BMS can read information from the boiler to determine its operating state, lockout
status, sensor readings, etc. A BMS can also operate the boiler by providing a setpoint.
Table 18-8: Modbus Configuration
Protocol
MODBUS RTU
Baud Rate
38400bps
Data Length
8
Parity
None
Stop Bit
1
Physical Layer
RS485 (2 wire)
Table 18-9: Supported Commands
DEC
HEX
Description
03
0x03
Read Holding Registers
04
0x04
Read Input Registers
06
0x06
Write Single Register
16
0x10
Write Multiple Registers
17
0x11
Report Slave ID
Table 18-10: Holding Registers (Read/Write)
Address
DEC (HEX)
Supported
Commands
Description
Byte:
Format
Notes
512
(0x00200)
0x03
0x06
0x10
CH Demand
MB:U8
LB:U8
Writing:
0= Modbus CH1 Demand has priority
over a DHW call.
255 = DHW call has priority over a
Modbus CH1 Demand.
Reading:
0 = No CH Calls Present.
255 = CH1 or CH2 Call Present.
Writing:
0 = End CH1 Demand.
255= Begin CH1 Demand.
A CH1 Demand lasts for 30 seconds
from the last successful write.
513 (0x201)
0x03
0x06
0x10
Maximum
Firing Rate
LB:U8
Value = Maximum Firing Rate %. This
register becomes active when 255is
written to register 512 (0x0200)
