PEERLESS PUREFIRE PFW-199, Installation, Operation & Maintenance Manual, Page: 78 / 81

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3. Modbus Holding Registers (Read/Write):
The 852-1 control has holding registers that allow
DHW Setpoints to be written using Modbus
commands. Table 8 shows the Modbus Holding
Registers for Read/Write Control.
4. Changing the DHW Setpoint:
a. Issue a Modbus write single holding register
command that writes 0x0001 to the R/W control
register located at 0x001A to switch the CH
setpoint reading to writing.
b. Calculate the scaled setpoint as follows:
(°C+10) x 2 = scaled value
c. Issue a Modbus Write single holding register
command to write the scaled temperature setpoint
value to the 0x001E holding register.
Table 8
Modbus Holding Registers (Read/Write)
Item Index
Parameter Name
Address & Holding Registers
Notes
Word byte
Range Start
0x0000
Range Start
0x0001
10 High byte 10 R/W control 0x001A 0x001B
(°C+10)x 2 = byte value
(°F– 32)x
5
9
=°C
10 Low byte 11 R/W control 0x001A 0x001B
14 High byte 14 NOT USED 0x001E 0x001F
14 Low byte 15 DHW_SETPOINT 0x001E 0x001F
If no Modbus command is sensed for more than 4.25
seconds after the Write Command is issued, the
control resets and the command must be re-issued
to change the setpoint.
NOTICE
If an invalid value is written after the Write Command
is issued, the control resets and the command must
be re-issued to change the setpoint.
NOTICE
Modbus setpoints are maintained in volatile memory.
Therefore, if the control must be reset due to an lockout
error, a new value for DHW must be written through
Modbus. If this is not done, the control will default to
the last value saved for each of these parameters.
NOTICE
The Infinite Energy main control resets automatically
every 24 hours. This will reset the CH and DHW
setpoint values to the last value saved for each of
these parameters. A new Modbus command should
be issued periodically for each setpoint to be sure
that the control is targeting the correct temperature.
NOTICE
If the setpoint is changed using the User Menu,
Installer Menu, SiteVision Software or Analog Inputs
(Infinite Energy DHW Mode 3), the Modbus setpoint
will be overridden. Frequent updates are required to
be sure that the control is targeting the correct
temperature.Be sure to set the System Test
parameter back to “Off” before leaving the
installation. Otherwise, problems with cycling or
insufficient heat may occur.
NOTICE
APPENDIX D. 852-1 INTERFACE ADAPTER