lp-548 Rev. 000 Rel. 004 Date 1.11.19
9
Table 9 - MODBUS Holding Registers
*The appliance will not respond to the internal DHW limit while the Tank Temperature AND Tank Enable is being written from
MODBUS/BACnet!
Part 5 - Appliance Operation
A. Appliance Operation with MODBUS and BACnet Communications
The appliance is equipped with a communication timer. Timeout is set for four minutes. The purpose of the timer is to ensure proper
temperature data is communicated to the appliance in a timely manner.
Additionally, the communication timer will provide fail safe operation should communication be lost. This timer will cause the appliance to
revert back to internal appliance controls should the communication be interrupted longer than the timer. The timer resets every time a write
command is received with updated temperatures or commands.
The master should update temperature registers at least once per minute, but no more than once per second.
Monitoring Only
Any appliance can be equipped with the MODBUS or BAC/net communication accessory and then be set up to operate with its own internal
controls. The master can then poll the MODBUS or BAC/net accessory for the read only variables. Refer to the following examples for
configuring the writable Holding Registers.
Holding Register 40002 / AV1
Selected Signal (Register) to Write to)
Coil 01 b0
1
01
Room thermostat
Coil 05 b4
16
10
Tank thermostat
B. Example #1 - Enable / Disable CH and DHW Demand
In this configuration, the appliance is controlled by setting the setpoints locally on the appliance and providing an enable signal through
MODBUS or BAC/net communications.
All sensors and limiting devices (excluding the thermostat enable and tank thermostat enable signals, which will be sent to the appliance)
should be hardwired to the proper terminals in the appliance. The holding registers need to be set as follows:
Holding Registers
Definition
Decimal
Value
HEX Value
Action
40001 / AV0
Configuration
3
0011
Set configuration to read 40002
40002 / AV1
Coils
1
0001
Enables CH Demand (00 00 disables demand) (boilers only)
40002 / AV1
Coils
16
0010
Enables DHW demand on appliance (00 00 disables demand)
40002 / AV1
Coils
17
0011
Enables both CH and DHW demand. DHW demand will have priority.
Table 10 - Example #1
Holding Registers
Definition
Decimal
Value
HEX Value
Action
40001 / AV0
Configuration
8
0010
Set configuration to read 40004/AV3
40004 / AV3
Coils
Setpoint
Setpoint
Directly writes setpoint to water heater
C. Example #2 - Sending DHW Setpoint Via Direct Write Method
Table 12 - Example #2
*The appliance will not respond to the internal DHW limit while the Tank Setpoint is being written from MODBUS/BACnet!
D. Example #3 - Sending Setpoint or Firing Rate from BMS
In this configuration, the appliance setpoint is indirectly controlled by sending a 0 to 10v signal to it. All sensors and limiting devices (excluding
1. Sending Desired Setpoint from BMS to Appliance Via Simulated 0-10V Method
Appliance
Parameter I16
Parameter I17
Phoenix, Munchkin, MODCON rev2 and earlier
2
0
Elite, Elite Premier, EnduroTi
0-10 Volt
Temperature
Table 11 - Send Desired Setpoint from BMS to Appliance
To send a desired CH setpoint on an appliance, or DHW setpoint on a water heater via 40003/AV2, the value (which equates to voltage applied)
must be determined through linear interpolation of programmable parameters on the BMS setup menu.
•
Appliance temperature setpoint at low analog input = MIN BOILER TEMP (I12) in the 925 Installer Menu
•
Appliance temperature setpoint at high analog input = CENTRAL HEAT in the 600 User Menu or PHOENIX in the User Menu
These variables set the temperature values corresponding to the minimum and maximum voltage settings of the 0 – 10 volt signal. The
defaults are as follows:
the 0 – 10 Vdc signal, which will be sent to the MODBUS/BACnet
adapter) should be hardwired to the correct locations on the
appliance.
For this command to function, configure the appliance
according to the corresponding row in the table to the right.
