> >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
>
> Hi,
> First of all, what do you mean HIGH on TX line on RS232 port of PC ?
> The TX and RX lines (in RS232) are not on TTL level.
> The 'logic 1' on TX (idle state) means this line is about -12V respect
> to ground, the 'logic 0' on TX (mark state) means this line is about +12V
> respect to ground.
> Apart from this, you can't change the state of TX in this way (to control
> relay).
> Instead of TX, use the RTS or DTR signal.
> These signals are TTLs, and it is easy to use as general purpose bits.
> To change these signals, set or clear the appropriate bit:
> (DTR)
> [baseaddr+4].0 (ie. base address of serial port, eg. com1=0x3f8,
> so the appropriate bit is the lsb of 0x3fc)
> (RTS)
> [baseaddr+4].1 (ie. base address of serial port, eg. com1=0x3f8,
> so the appropriate bit is the second bit of 0x3fc)
>
> bye
> csaba
>

The baseaddress can be found in the ROM BIOS parameter area at
addresses:

0000:0400 COM1
0000:0402 COM2
0000:0404 COM3
0000:0406 COM4
0000:0408 LPT1
0000:040A LPT2
0000:040C LPT3
0000:040E LPT4

The ones that doesn't exist have 0 as baseaddress.

--------------------------------
Ruben Jvnsson
maxruben@mail.bip.net
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