Re: Another clueless question...
From: toa (to_ape_at_hotmail.com)
Date: 11/05/04
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Date: Fri, 5 Nov 2004 06:47:05 +0100
"Dbowey" <dbowey@aol.com> wrote in message
news:20041105132223.08281.00000156@mb-m04.aol.com...
> toa posted:
> << I'm trying to make sense of an RS232 card that I took from an old PC,
which
> necessitates my understanding of the PC's ISA bus architecture. I'll be
> connecting the card to some custom-made circuitry instead of the ISA bus.
> Most of what I've learned about it so far seem straightforward, but the
one
> thing I'd like to get a tip on, is the power supply. In addition to +5V
and
> Ground, the card requires a +12V input and, worse, a -12V input. What is
the
> standard way of providing these voltages? All I have so far is a power
> supply offering one output tha can be varied continuously from 0 to 30
> volts. So, do I actually need 3 power supplies, or what? >>
>
> --
>
> The standard way of providing the voltages is by using the PCs power
supply, or
> buy or scrounge a computer power supply. They have one or more of:
12V, -12V,
> and 5V. These supplies commonly require a minimum load on each output in
order
> to work correctly.
>
> You should not be surprised at the need for +12V and -12V, as classical
"RS232"
> require both polarities, where - is mark (1) and + is space (0).
>
> Don
Oh, I'm not surprised, just at a loss as to how to proceeed. Until now, that
is. I guess I'll go butcher my old 386 some more, then. Any idea what that
"mimimum load" might be? I suppose I should wire some heavy-duty resistors
in parallel with the card then?
Anyway, thanks a lot for your input - hopefully it will get me going again.
:)
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