SATELLINE-3AS
User Guide, Version 2.3
32
5.2 Handshake lines
When using the RS-232 serial interface, handshake signals can be used to control data transfer.
Handshake signals are used, for example, by the radio modem to inform the terminal that the
radio channel is busy, and that it cannot initiate transmission. The terminal can also control the
radio modem via RTS-line.
Line
Direction
CTS To
terminal
RTS To
modem
CD To
terminal
A common way of using handshaking signals, is to monitor the CTS-line and ignore the others.
Usually the terminal is fast enough to handle the data received by the radio modem, so the use
of RTS-line is not necessary.
Handshaking is not needed if the system protocol is designed to prevent collisions (data
contention) by the use of polling, or if there is little traffic and also if there is no harm from
occasional data contention situations (several radio modems try to transmit at the same time).
5.2.1 CTS-line
The options for CTS-line are:
1) C
Clear To Send
Operation is similar to SATELLINE-2ASxE. CTS is active when the radio modem is ready to
accept data for transmission. CTS will shift into inactive state during data reception, and when a
pause (packet end) is detected in transmitted data. CTS shifts back into active state either when
reception ends, or the radio modem has finished transmission. CTS will also shift into inactive
state where the serial interface data transfer speed is greater than the radio interface transfer
speed, and if the transmit buffer is in danger of overflowing.
2) T
TX buffer state
CTS will shift into inactive state only if the radio modem transmit buffer is in danger of
overflowing.
5.2.2 CD-line
The options for CD-line are:
1) R
RSSI-threshold
Operation is similar to SATELLINE-2ASxE. CD is active whenever a signal with a level exceeding
the level required for reception exists on the radio channel. It doesn’t make any difference if the
signal is an actual data transmission, a signal of a radio transmitter not belonging to the system,
