Rev. 0B
10
Transmit/Receive Operation
The SD250 is put into transmit/receive either by using TTL levels, RS 232 levels
or serial command, depending on the application and modem set up.
When the radio is used with no internal modem, TTL levels (pin 3 on DB9) can
be used. The default condition is active low for transmit, and active high, or not
connected, for receive. It is possible to alter the polarity of this control signal by
adding components, refer to the pin out table for details.
If an internal modem is fitted the levels used need to be RS232 and a resistor link
needs to be incorporated in the correct position to allow correct operation, see
modem manual.
The TX serial command (see later for further details) can also put the radio into
transmit, until the RX serial command is received (pin 8 of DB9).
Serial Commands
The RF data module can be controlled by using the serial command (pin 8) ,
sending commands to the radio such as PTT or change channel
The format for these commands (asynchronous) are:
• baud rate: 9600 bit/sec
• Data Bit: 8 bit, non parity
• Stop Bit: 1 bit
• MSB first transmission
Each serial command consists of 3 bytes. The first byte is the command, the
second is data required by the command and the third is the check sum to
validate contents
Summary of Contents for SD-250
Page 1: ...SD 250 User Guide...