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ARF868 Radio Modems - Guide utilisateur / User guide version V2.2.3
4. Advanced product functions
4.1. UART interface self-detection
The ARF868 modem has automatic interface detection at switching on enabling a selection of the RS232 or RS485 mode. Automatic detection is
activated when interface selection register S215 is positioned on the value 4.
For detection in the RS485 mode it is essential to have an earth connected to the product. Otherwise the detection motive "U" cannot be taken
into account.
FR
4.2. Auto-baud: Self-detection of the serial link data rate
On switching on with the SubD9 cable connected, the modem detects the data rate on the serial link of the monitoring equipment in order to
synchronise itself on its parameters.
For this detection to be performed, the equipment must send, before any command or character chain, the synchronisation command: " U "
After a positive reply from the modem, it is then operational and switches to the communication mode. It will be capable of transferring the
EN
characters seen on the serial link onto the Air link or entering the command mode (see § 5.2 command mode input/output).
Command
U (upper case)
Note :
To this request the modem will reply by the configuration that it has detected: type of link, UART data rate. E.g.: RS232, 9600.
If the modem does not reply or replies by another character chain to the synchronisation request U, a new test can be attempted, after having
disconnected and reconnected the electricity supply to the appliance. If these attempts produced no effect, check that the serial link of the mon-
itoring equipment is set to: 8bits, 1 stop bit, no parity and that the UART proposed corresponds with one of the data rates available in register
S210.
Sending of the synchronisation character "U" is only useful on first switching on or as long as a UART configuration has not been memorised on
registers S210 by the AT&W command.
On equipment that is already synchronised, it will not be interpreted as a synchronisation request and will be transferred onto the air link like
any other character chain.
The self-detection mode (type & data rate) will be retained for the next switching on in the following three situations:
•
No saving of register S210 by the AT&W command before switching off.
•
Brief pressure on BP1 before the power is cut off
•
Return of register S210 to the value of 0 by ATR and AT&W commands before the power is cut off.
4.3. RSSI
The Received Signal Strength Indication or RSSI provides an indication of the RF level in the selected audio channel.
Depending on the value observed, it indicates the availability of the channel and the noise level in the product's environment, or the quality of
reception of the frames from a distant product. The terminals are -127dBm for the lower limit and -20dBm for the upper limit
The RSSI is deactivated (by default) by positioning register S230 at: 0
4.3.1 Continuous RSSI
The RSSI is coded on one octet in absolute values of the channel level value in dBm and transmitted to the UART. The RSSI is refreshed continu-
ously every 10 ms. There is no frame demodulation in this mode.
Register settings and values
Selection of the continuous RSSI mode is done by register S230, by setting the value to: 4
4.3.2 Frame RSSI
The frame RSSI is the code on one octet at the beginning of each frame transmitted on the UART. The encoding is identical to the continuous
RSSI.
Register settings and values
Selection of the continuous RSSI mode is done by register S230, by setting the value to: 1
4.4. Scan Free function
The Scan Free function is a function that is unique to ARF868 modems.
Description
Allows automatic detection of UART data
rate (see note 1).
Answer
Returns the parameters of the serial link :
RS232 or RS485 and data rate.
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