Detcon RXT-320 - Manual (Page 22)

RXT-320 Wireless Modbus ™
RXT-320 Wireless IM Rev. 2.1 Page 18 of 27
rather to drive relay coils which in turn will drive a higher current output. There are four RXT alarm output
registers that become available when in alarm station mode. The four alarm outputs are controlled by four
internal registers within the RXT-320 and can be controlled on all RXT-320 transceivers by writing to these
four registers using the Modbus™ address assigned that transceiver.
If the RXT-320 transceiver is assigned a Modbus™ address between (80h-8Fh) there will be a duplicate set of
four registers available to control the alarm outputs.
These are introduced for compatibility with some
controllers.
NOTE: If the transceiver is assigned a Modbus™ address between E0h-EFh on the Term
board the RXT-320 will remap its address to the 80h-8Fh address respectively and function the
same way.
3.5 Sleep Mode
A sleep mode is available to increase the battery life of the RXT-320 transceiver assemblies that have them.
Upon command from the Modbus™, all RXT-320 transceivers will turn off their wireless radios for the
requested period of time. During this time there will be no communication possible with other RXT-320
transceivers. The command is given through a single Modbus™ broadcast command (Modbus™ address of 0)
with the number of seconds to go to sleep. Every RXT-320 transceiver that receives this command will turn
off their on-board radio and count down the seconds until it reaches zero at which time the radios will be
turned back on. The controller can query the sleep timer on its own transceiver to determine how many
seconds are left and can begin Modbus™ communication when it reaches zero.
NOTE: Sleep mode is not supported by transceivers that are in transparent mode since no
address is assigned and therefore its internal registers are not accessible through Modbus™.
When the RXT-320 transceiver radio is put to sleep it will reduce the RXT-320 power consumption by about
90%. This of course does not include other devices running off of the battery, only the transceiver. Generally
the controller will put the network to sleep after all devices have been polled on the network. While the
network is asleep, there are no devices being read so the user will have to trade off power consumption versus
the time between updating/reading a device on the network.
4.0 Modbus Communications
The RXT-320 wireless transceiver incorporates an RS-485 two-wire interface for communication with various
Modbus™ devices such as a control system or sensor. There can be up to 32 devices attached to an RXT-320
wireless transceiver and up to 32 RXT-320 transceivers on a single wireless network.
As with normal
Modbus™ operation, there can be only one Modbus™ master that polls all the other devices which are
considered Modbus™ slaves. Each slave device must have a unique Modbus™ address.
The Modbus™ master control unit with its transceiver is responsible for broadcasting requests and receiving
slave device responses. Slave device transceivers receive these broadcasts and pass the Modbus™ requests on
to the slave devices attached. When a response is generated by the slave device, its transceiver transmits the
response back to the broadcasting transceiver, which then places the response on the bus back to the master
control unit. Modbus™ communication is accomplished by two wire half duplex RS-485, 9600 baud, 8 data
bits, 1 stop bit, no parity, through the transceiver’s connection to the Modbus™ device.