Craig Webb wrote:
>
> Does anyone know off-hand the memory address and value for setting the RS232
> TX line high on a PC? I need to trigger a relay connected to this line.
>
> Thanks.
>
> C. Webb

Probably better to use the DTR or RTS lines for this sort of job, as
they are direct digital outputs. Set them HI or LO by writing to the
MCR (Modem Control Register) in the PC's UART.

MCR bit 0 drives DTR
MCR bit 1 drives RTS

The address of the MCR is 03FCh, for COM1 where base-address is 03F8h,
use same offset if other port at other base address.

Hope this is of use
jim ford