ETIC MR1200, Руководство пользователя

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Operation
ETIC - MR1200 - USER MANUAL - 908709-02 Page29
4. OPERATION
4.1. Principle
Communication between MR1200 and control terminal takes place over the RS232 serial link. The
modem then obtains access to the radio channel and finally sends the data to be transmitted.
•
Call control :
4 control modes enable the terminal to control the modem.
The MR1200 then checks the status of the radio channel, turns on a relay if appropriate and
finally transmits the data.
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Data Communication : Data transmission over the radio channel is half duplex.
Communication between the modem and terminal is duplex.
4.2. Radio channel
4.2.1. Data transmission method
The MR1200 radio modem adheres strictly to the specifications laid down in the French standard
ST/PAA/DIR/1382.
Radio channel data transmission is synchronous and uses a data rate of 1200 or 2400 b/s.
The modulation employed is of an indirect type : an FFSK modulated audio frequency sub-carrier
phase modulates a radio frequency carrier.
Normal transmission is in « base mode » : data to be transmitted is formatted into frames protected by a
cyclic redundancy check code (CRC), giving a useful radio channel data rate of 900 b/s.
Another transmission mode without CRC, called « simple mode », is also available but should not be
employed unless the radio link is of good quality (communicating stations relatively close), and where
a useful radio channel data rate greater than 900 b/s is essential. The data is transmitted without any
extra coding and errors are no longer filtered out on reception of data.