DECODE PRM4 Посібник користувача - Сторінка 5

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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