PureFire PFA-1 Interface Adaptor Installation, Operation, and Maintenance Manual

7
PUREFIRE PFA-1 INTERFACE ADAPTER
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 CH and 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 P URE F IRE 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
(
P URE F IRE Control CH Mode 4 and Mode 5), the Modbus setpoint will be overridden. Frequent updates are
required to be sure that the control is targeting the correct temperature.
NOTICE
3. Modbus Holding Registers (Read/Write):
The PFA-1 control has holding registers that allow
CH and DHW Setpoints to be written using Modbus
commands. Table 8 shows the Modbus Holding
Registers for Read/Write Control.
4. Controlling Main Board Parameters:
a. To change the CH setpoint
:
- Issue a Modbus write single holding register
command that writes 0x0002 to the R/W
control register located at 0x001A to switch
the CH setpoint reading to writing.
- Calculate the scaled setpoint as follows:
(°C+10)x2x256=scaled value
- Issue a Modbus Write single holding register
command to rite the scaled temperature
setpoint value to the 0x001E holding register.
b. To change the DHW setpoint
:
- 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.
- Calculate the scaled setpoint as follows:
(°C+10) x 2 = scaled value
- 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 CH_SETPOINT 0x001E 0x001F
14 Low byte 15 DHW_SETPOINT 0x001E 0x001F