Supplementary User Guide

57
8.0 Modbus Interface
8.0 MODBUS INTERFACE
The Modbus Interface allows a Building Management System (BMS) to directly connect to the Prestige.
A BMS can read information from the boiler to determine its operating state, lockout status, sensor read-
ings, etc. A BMS can also operate the boiler by providing a setpoint.
Table 7: Modbus Configuration
Protocol MODBUS RTU
Baud Rate 38400bps
Data Length 8
Parity None
Stop Bits 1
Physical Layer RS485 (2 wire)
Table 8: 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 9: Holding Registers (Read/Write)
Address
DEC (HEX)
Supported
Commands
Description Byte: Format Notes
512 (0x0200) 0x03
0x06
0x10
CH Demand MB:U8
LB:U8
Writing
0= Modbus CH1 Demand has prior-
ity 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
255 is written to register 512
(0x0200)
514 (0x202)
0x03
0x06
0x10
CH Setpoint
LB:U8
Value = CH Setpoint °C
This register becomes active when
255 is written to register 512
(0x0200)
1280 (0x0500)
0x03
CH1 Maximum
Setpoint
LB:U8
Value = °C
1281 (0x0501)
0x03
DHW Storage
Setpoint
LB:U8
Value = °C