Detcon RXT-320 - Manual (Page 21)

RXT-320 Wireless Modbus ™
RXT-320 Wireless IM Rev. 2.1 Page 17 of 27
NOTE: Transparent mode does not support accessing the internal registers of the transceiver
through Modbus™ since there is no address assigned. Consequently many features are not
available such as sleep, battery status, 4-20mA inputs and alarm outputs.
3.2 Master Configuration with Controller
The RXT-320 wireless transceiver can function as a master when connected to a controller by assigning it a
Modbus™ address of F0h through the transceiver’s Model 100 Terminal Board. In this configuration, the
controller can send out requests and receive data/status from slave devices over the wireless network through
its Modbus™ interface to the transceiver. The transceiver’s local Modbus™ interface is set up to be a slave
interface to the master controller which means the transceiver will act as a slave to the controller but be seen as
the master globally. Requests from the controller will be received by the transceiver through the Modbus™
interface and the transceiver will transmit the request over the RF network to all RXT-320’s. If the slave
device being commanded is found, a response will be generated which will be received by the master
transceiver over the RF network and sent back to the controller via the local Modbus™ interface.
3.3 Slave Configuration with Sensor
The RXT-320 wireless transceiver can also function as a slave when connected to a slave device (sensor) by
assigning it a Modbus™ address that is not equal to F0h (controller) or 00h (transparent mode).
This
Modbus™ addressing will affect how the slave RXT-320 deals with the request it receives. In this
configuration, the transceiver can receive requests and send out data/status over the wireless RF network. The
transceiver’s local Modbus™ interface is set up to be a master interface to the slave device which means the
transceiver will act as the master to the sensor attached but be seen as a slave globally. Modbus™ addressing
will dictate how the transceiver deals with a request.
If the Modbus™ address in the request does not equal the address assigned to the RXT-320, the transceiver
simply sends along the request unchanged on to its Modbus™. It will behave similar to transparent mode.
The request will be responded to if a sensor with an address equal to the address in the request is found. If so,
the sensor will respond back to the transceiver via Modbus™ which will then send the response back to the
controller over the RF network.
If the Modbus™ address in the request equals the address assigned to the RXT-320 and does not fall within the
RXT-320 internal registers, the transceiver will translate the Modbus™ address to 01h and send along the
request on its Modbus™ interface with the new translated address. This translate function allows a single
DM-100 sensor to be installed per each RXT-320 since all DM-100 sensors have a fixed address of 01h. If a
sensor with an address of 01h is found, it will respond back to the transceiver via Modbus™. The transceiver
will then translate the 01h address back to its original value and send the response back to the controller over
the RF network.
If the Modbus™ address in the request equals the address assigned to the RXT-320 and falls within the RXT-
320 internal registers, the transceiver will not translate. The transceivers RXT-320 registers will be accessible
and it will respond back to the controller over the RF network without ever having put any data on the
transceivers Modbus™ interface. Any sensors connected to the transceiver would never see the request.
3.4 Slave Configuration with Alarm Station
Another function of the RXT-320 wireless transceiver is as an alarm output device when connected to an
alarm station. Each RXT-320 provides up to four alarm outputs (Alarm 0, Alarm 1, Alarm 2 and Alarm 3)
which can drive relays on custom terminal boards provided by Detcon or interposing relays provided by the
customer. These outputs are not intended to drive alarm devices directly due to their low current output, but