2 Modes of operation
Decode PRM4 device can operate in one of the two modes of operation.
When powered, the device will automatically enter the default,
data transfer
mode.
When the device is in the
data transfer
mode, it will listen and receive all the packets
intended for it, whereas the transmitter will turn-on only occasionally to send the data
acquired from the wire connection.
The mode and parameters of operation are set through the use of AT commands using
the
command
mode
of operation. The transfer into the
command
mode and the set of
supported AT commands is described in chapter 4.
The PRM 4 device supports an addressing scheme. All modems intended for data
exchange in a radio network must be set to the same frequency and must have the
same
network address
(NA). The NA can be set to any value from the 0 – 65535
range. Each device has its
source address
(SA) used to identify the device inside a
network. The SA can take values between 0 and 255 inclusive. Note that the SA must
be set uniquely inside a network. If a point-to-multipoint connection is required (e.g.
for master-slave protocols used with SCADA software or PLC devices) the
destination address
(DA) masking is used. This way it is possible to mask a number
of bits when comparing the DA and SA and, consequently, the packet with one
destination address can be sent to multiple devices having the unmasked parts of their
SA match the unmasked parts of DA.
For example, if assumed that the radio frequency and the NA are the same for all the
devices in the following figure, the device with the SA equal to 100 will send its
packets to the remaining three devices, whereas the devices with the SA 1,2 and 3 will
send data only to the SA 100 device. This is because the
Address Masks
(AM) on
devices with SA 1,2 and 3 have been set to 252 (binary 11111100) so that they match
the higher (unmasked) six bits of the DA (binary 000000).
Radio modem PRM4 868MHz /User's manual V1.6 / 24.05.2011
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