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COMMUNICATIONS PROTOCOL OF THE DATA DISPLAY SYSTEM AND
B.1 Data frames exchange between the detecting unit and the data display system is done via the
RS-485 interface in a half-duplex mode.
Exchange parameters:
- rate: 19200 bps;
- data word length: 8 bit;
- parity bit: none;
- stop bit: 1.
Time interval between the bytes in one frame should not exceed 1 ms. Time interval between the
frames should not be less than 5 ms.
B.2 After the supply voltage from the data display system is transmitted to the detecting unit, the
latter not later than in 30 s automatically starts gamma radiation DER measurement and processing
of data frames form the data display system.
B.3 This detecting unit supports data communications protocol version with both 4-digit filed
address (v1.2), and 8-digit field address (v1.3).
B.3.1 Communications protocol with the 4-digit field address (v1.2).
To receive the measured value of DER from the detecting unit, the data display system should
transmit the "DER query" frame to the detecting unit. The detecting unit will respond in 5 ms to
15 ms with the "Current DER" frame, where current DER, maximum statistical error of its
measurement, and self-testing results of the detecting unit will be displayed.
To receive the measured value of temperature from the detecting unit (with embedded temperature
detector), the data display system should transmit the "Temperature query" frame to the detecting
unit. The detecting unit will respond in 5 ms to 15 ms with the "Current temperature" frame, where
current temperature and condition of the temperature detector will be transferred.
To receive the serial number of the detecting unit, the data display system should transmit the
"Serial # query" frame to the detecting unit. The detecting unit will respond in 5 ms to
15 ms with the "Serial #" frame with the displayed serial number.
To change the address of the detecting unit, the data display system should transmit the "Address
change" frame to the detecting unit. In 5 ms to 500 ms the detecting unit will respond with the
"Confirmation" frame. Caution! In the address field of the "Confirmation" frame the old value of
address will be recorded. In the event of successful reception of a new value, the detecting unit records
it in the nonvolatile memory, and not later than in 5 s starts responding to the frames with a new
address.
To make operation with several detecting units (up to 15 units) easier that are simultaneously
connected to the data display system via single RS-485 interface, the 0Fh broadcast address is
provided. The use of this address is permitted only in the "DER query", "Temperature query" and
"Serial # query" frames. All detecting units respond to the query with such address (broadcast
query).
When the detecting units respond to the broadcast query, each of them does it with delay T, which
is calculated by the formula:
where Adr is the address of the detecting unit.
The broadcast query also enables easy realization of autodetection of the detecting units that
connect/disconnect to/from the data display system in the process of system operation.
APPENDIX B
THE DETECTING UNIT
T = 5mS + Adr × 8 mS,
26
(B.1)
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