Re: How can I write to a PC port through dos

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#791

From: Lawrence Kirby
Date: Mon, 28 Dec 1998 00:00

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In article <3686F719.327E6798@ipns.com> mikeyyou@suck.ass "James Connell" writes:

>actually DOS has nothing to do with it!

Quite the opposite, knowing that you are programming in a DOS environment is
critical for any correct answer for this problem.

>the Intel prossor has an in and
>an out instruction to write a byte or word (also strings) to one of 64K
>IO ports pointed to by the DX register ( or by an 'Immediate' operand
>for the first 256).

However most of the better OSs arrange for these instructions to be invalid
(i.e. cause exceptions) for user level code. And of course even if you
can access hardware directly doing so may clash with the OSs own drivers.

>while not opsys dependant it is system dependant.

The question is fundamentally opsys dependent, it *cannot* be answered other
than with respect to a specific OS and even specific environment within that
OS (user level code, device driver etc.)

-- 
-----------------------------------------
Lawrence Kirby | fred@genesis.demon.co.uk
Wilts, England | 70734.126@compuserve.com
-----------------------------------------

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From: fred@genesis.demon.co.uk (Lawrence Kirby)
Subject: Re: How can I write to a PC port through dos
Date: 1998/12/28
Message-ID: <914876095snz@genesis.demon.co.uk>
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