
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
2015-10 Prestige ACVMax Control Sup 12-14-15_ACVMax_Control 12/15/15 7:38 AM Page 57