16
HOLDING REGISTERS
DEFINITION
VALUE
ACTION
40001
Configuration
00 04
Set configuration to read 40003
40003
Rate Command
00 00
Sets modulation %
Table 16
Register 40003 needs to receive the rate command as follows: Acceptable rang is 0 to 100. Value needs to be greater than 15
for the boiler to fire. When the command is 16, the boiler will run at minimum fan speed (firing rate). When the command is
100 the boiler will run at max fan speed (firing rate). If the command value is anywhere between 16 and 100, the boiler will run
at a fan speed proportional to the command sent between minimum and maximum firing rates.
NOTE:
To ensure proper operation, resend the configuration bits to holding register 40001 prior to issuing a command. For proper
hexadecimal conversion of rate percentage, please refer to the rate and temperature conversion section of this manual.
2. SEND TEMPERATURE COMMAND FROM MASTER
In this configuration, the appliance is controlled by setting the boiler temperature via the Modbus adapter. The temperature range is the
range of the value of Installer Parameter 12 (all except Elite) or Function 12 Min Boiler Temp on the Elite, and the temperature setting
of the CH value on the User Menu (all except Elite) or CENTRAL HEAT setting on the Elite. All sensors and limiting devices (excluding
the 0-10 Vdc signal, which will be sent to the Modbus) should be hardwired to the terminal strip on the appliance.
For this command to function on Munchkin and Mod Con models, Installer Parameter 16 needs to be set at 2 and Installer Parameter
17 needs to be set at 0. On Elite models, Function 16, Optional Input must be set to 0-10 volt and Function 17 0-10 volt function must
be set on Temperature.
NOTE:
The holding registers are same as above, in Table 15.
Register 40003 needs to receive the rate command as follows: Acceptable rang is 0 to 100. Value needs to be greater than 15
for the boiler to fire. When the command is 16, the boiler will run at minimum temperature (value of Installer Parameter 12
above). When the command is 100 the boiler will run at maximum temperature (CH temperature above). If the command value
is anywhere between 16 and 100, the boiler will run at a temperature proportional to the command sent between minimum and
maximum temperatures described above.
NOTE:
To ensure proper operation, resend the configuration bits to holding register 40001 prior to issuing a command. For proper
hexadecimal conversion of rate percentage, please refer to the rate and temperature conversion section of this manual.
D. EXAMPLE #3
– HOT WATER GENERATION
Hot water generation can be accomplished using one of two methods when an appliance is connected to a BAS system, DHW with
direct control, and DHW with remote control.
DHW WITH DIRECT CONTROL
This is the typical installation with a hot water generator in close proximity to the appliance with the tank thermostat, or tank temperature
sensor, wired to the terminal strip of the appliance
DHW WITH REMOTE CONTROL
This installation may or may not have the hot water generator in close proximity to the appliance. Its sensors and thermostat values are
only available through the Modbus communication bus.
To ensure that the appliance can properly respond to a call for hot water generation, the following holding registers must be set in
addition to other commands:
HOLDING REGISTERS
DEFINITION
VALUE
ACTION
40001
Configuration
00 1A
Set configuration to read 40002, 4 and 5
40002
Coils
00 10
Enables tank Tstat
(00 00 disables appliance)
40004
Tank set point
0# ##
Sets set point
40005
Tank Temperature
0# ##
Passes tank temp from remote sensor
Table 17
NOTE:
To ensure proper operation, resend the configuration bits to holding register 40001 prior to issuing a command. For proper
hexadecimal conversion of rate percentage, please refer to the rate and temperature conversion section of this manual.
E. CASCADE
In order to operate the appliance in cascade with Modbus communications, configure the master appliance. Connect the remaining
appliances in the cascade through the normal cascade communications wiring. Cascade control can then be accomplished
automatically through the master appliance.
