User guide

SATELLINE-3AS NMS / NMS Epic / NMS 869 / VHF
User Guide, Version 1.0
36
5.6.5
DSR line
DSR (Data Set Ready) is a signal from the radio modem to the DTE. It indicates that the radio
modem is powered up. DSR is typically ignored.
5.7
Pause length
The radio modem recognizes a pause on the serial line (a pause is defined as a time with no
status changes in the TD line). The pause detection is used as criteria for:
- End of radio transmission - When the transmit buffer is empty and a pause is detected, the
modem stops the transmission and will change the radio to the receiving mode
- SL command recognition - For an SL command to be valid, a pause must be detected before
the actual “SL“ prefix of the SL command.
- User address recognition
In order for detecting the message, a pause must precede it in transmission.
Traditionally, in asynchronous data communication, pauses have been used to separate serial
messages from each other. However the use of non-real-time operating systems (frequently used
on PC type hardware) has changed this tradition by adding random pauses in the
asynchronous data stream. Such systems can’t serve the hardware UART properly when
performing other tasks (other applications or tasks of the operating system itself).
The pauses described above are typically up to 100 ms. When such a pause appears in the
middle of a user message, the radio modem transmits the message as two separate radio
transmissions. This will generate problems in at least two ways:
1) The inter-character delay will be increased by at least the time of the modem transfer delay
2) The probability of collisions on the radio path will increase. This will be especially harmful
for repeater chains
The default value for the Pause length is 3 bytes.