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HW PROTOcOL INSTALLATION GUIDE
Modbus Configuration
The list of supported Modbus function codes and the Modbus Point Map are in the
Point Map section of this document. The capabilities for controlling the TWxP are
identical with those for BACnet. The functions are summarized here.
Function Description
Coils Used to set temperature (Fahrenheit scale) and override button coil. *
Discrete
input
Indicates whether the relay is on.
Input
registers
Used to read the sensor options: RH (in units of 0.1%), temperature (in units
of 0.1°), and the slider (in units of %full scale). **
Holding
registers
Used to specify the temperature oset and RH oset. Initial settings are 0°F,
and 0%, respectively. Settings are retained if power is lost.
* The temperature scale is maintained if power is lost. When delivered, temperature in Farenheit
and calibration lockout is on. Pressing the override button turns the override button coil on. It can
only be turned o remotely.
** If any sensor option is not installed, the reading for that sensor will be 0.
The various registers are still present even without the corresponding options
installed. In particular, the discrete input function can be used to see if the CO2
setpoint has been reached even if the relay is not in use.
BACnet Configuration
The list of BACnet objects and their implemented properties is in the BACnet
Descriptions section of this document. The capabilities for controlling the CWxP
are identical with those for the Modbus conguration. However, BACnet has some
additional protocol-related settings.
The Device Object must have a unique name. This is set at the factory to the model
name, followed by the device’s serial number. The name can be changed if desired.
The device object must also have a unique object identier number. By default, this
is 133nnn where nnn is the current network address. This number can be changed
and the new number will be remembered. Setting the number to -1 (normally not
allowed) will reset the device to the default.
The Reliability property of the analog inputs for temperature, relative humidity, and
slider can be read to determine whether the device has these options installed.
8. Install the sensor onto the backplate.
9. When installation is complete, install the cover
and snap into place.
VISUAL INDICATORS
The RX light will ash while data is being received. If it isn’t blinking, it can indicate a
bad connection or that the RS-485+ and RS-485– wires are connected backwards.
The TX light will ash while data is being transmitted. For Modbus, if this light isn’t
blinking it can mean that the device isn’t being selected (wrong address) or the
communication parity or bit rate is set improperly.
In a BACnet installation, both the RX and TX lights will ash repeatedly even if no
communication is being performed. In a Modbus installation, no lights will ash if
there is no communication activity.
MODBUS POINT MAP
Function code Function
01 Read coils
03 Read holding registers
04 Read input registers (if any sensor is not installed, the reading for that
sensor will be 0)
05 Write single coil
06 Write single register
07 Diagnostics (sub-function 00 returns query data)
15 Write multiple coils
16 Write multiple registers
17 Report slave ID (returns manufacturer, model name, and serial number)
All of these values correspond to BACnet objects with the same name. See the BACnet
Descriptions section for denitions.
Coils
1 Fahrenheit (else Celsius)
2 Override (use override button to turn on)
Input Registers
1 Humidity (in tenths of a percent)
2 Temperature (in tenths of a degree; units set by coil 1)
3 Slider (in percent)
Holding Registers
1 Temp Oset (in tenths of a degree, current units)
2 RH oset (in tenths of a percent)
