WSN Manual
Page 18 of 34
Rev. G
– 4 March 2007
Transmission Without Hardware Handshaking (RS232-Only and TTL Versions):-
If RTS/CTS handshaking is disabled the radio will start transmission as soon as data is received
at the serial port, transmission ceases as soon as the serial buffer has been emptied and a
period equivalent to two characters at the radio signal baud rate has elapsed. It is important to
note that since transmission ceases as soon as a two-character delay in the incoming data
stream is seen, data characters in a message must be presented in a continuous back-to-back
stream.
In this mode CTS is still used to indicate the serial buffer fill level in the same way as described
in the section on transmission using handshake, the difference is that in the idle state CTS is
always active indicating readiness to accept data. In most applications CTS can be ignored as
messages are likely to be smaller than the serial input buffer (1k byte), bear in mind also that if
the radio baud rate and data format is the same as that configured for the serial port the buffer
is being emptied as fast as it is being filled and so buffer overrun is unlikely.
5.13.3 Data Reception
Any data received by the radio is simply output to the serial port, and in RS232 configurations
the DCD line can be programmed to operate in three different modes to assist the host. Firstly
by indicating that a carrier is detected on the radio channel, this is useful if a busy lockout
function is required (although this can be dangerous if the channel is susceptible to interference
as well as wanted signals), secondly DCD can indicate presence of a carrier and a valid data
signal, data will normally be output under this circumstance, the third mode behaves in the
same way as the second except that DCD remains active until all data has been output to the
serial port after the signal has gone, this allows DCD to be used as a wake up signal.
In RS422 and RS485 2-wire configurations, the radio will output data on to the 2 wire circuit
whenever it is received, which could lead to a bus conflict in conditions of high interference,
preventing any connected terminal from transmitting data when it wants to. To avoid this
condition it is recommended that the message packeting option is turned on at both ends of the
radio link in this mode.
