BBC BASIC Programmers' Reference

by Richard Russell, July 2007

Occasionally you may wish to send a break condition on a serial port output line. For example this may be needed to 'wake up' a remote device such as a modem. You can easily do that using the following code:

        SYS "SetCommBreak", @hfile%(com1%)
        WAIT 50
        SYS "ClearCommBreak", @hfile%(com1%)

Here com1% is the value returned from OPENUP when the serial port was opened. In this example the break condition is maintained for about 0.5 seconds (50 centiseconds).

For completeness here is a self-contained program which opens the port, sends the break, and then closes the port:

        com1% = OPENUP("COM1:9600,n,8,1")
        IF com1% = 0 ERROR 100, "Couldn't open serial port COM1"
 
        SYS "SetCommBreak", @hfile%(com1%)
        WAIT 50
        SYS "ClearCommBreak", @hfile%(com1%)
 
        CLOSE #com1%