Satel EASy+ - CTS Line; CD Line

SATEL-EASy+
User guide
Version 1.33
27
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).
5.6.1 CTS line
CTS (Clear to Send) is a signal from the radio modem to the DTE. It indicates when the radio
modem is ready to accept more data from the DTE. The options for CTS line are:
• Clear to Send - CTS line is set active when the radio modem is ready to accept data for
transmission. CTS will shift into inactive state during data reception, and at the end of
transmission. CTS shifts back into active state either when reception end or the radio
modem has finished data transmission. CTS will also shift into inactive state when the
transmit buffer is about to overflow i.e., there is more data coming in from the serial port
than the radio is able to transmit.
• TX buffer state - CTS will shift into inactive state only if the radio modem’s TX buffer is
about to overflow. This typically happens when the transfer speed on the serial interface
is greater than on the radio interface, and the size of transmitted messages is large.
• CTS line properties: Duty cycle, Always ON and RSSI Threshold are reserved for future
purpose.
5.6.2 CD line
CD (Carrier Detect) is a signal from the radio modem to the DTE. It indicates when there is
activity on the radio channel.
• RSSI-threshold - CD is active whenever a signal exceeding the level required for reception
exists on the radio channel. It does not make any difference if the signal is an actual data
transmission, a signal of a radio transmitter not belonging to the system, or even an
interference signal. CD is also active when the radio modem itself is transmitting.
NOTE: Due to the shared pin configuration on D15 connector, CD signal is not available if Serial
Port 2 is used for data transmission.
NOTE2: If Serial port 2 is in RS422/485 mode, CD signal is not available.