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From: kneller@cgl.ucsf.edu (Don Kneller)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Where is the paralell port???
Message-ID: <11272@cgl.ucsf.EDU>
Date: 13 Dec 88 23:32:29 GMT
References: <10690@s.ms.uky.edu> <424@megatek.UUCP>
Sender: daemon@cgl.ucsf.edu
Reply-To: kneller@socrates.ucsf.edu.UUCP (Don Kneller)
Organization: UCSF Computer Graphics Lab
Lines: 33

In article <424@megatek.UUCP> hollen@spot.megatek.uucp (Dion Hollenbeck) writes:
>> In article <464@octopus.UUCP> pete@octopus.UUCP (Pete Holzmann) writes:
>>>be ignored. LPT1 is at whatever I/O address is stored in the 16 bits at
>>>40:8, LPT2 at 40:0a, etc.
>>>
>>>unsigned far *lpts = 0x00400008L;  /* Define a pointer to the LPT ports */
>>>unsigned LPT1Base = lpts[0];
>>>
>> 
>FAR or HUGE >pointers are stored by MSC and TURBO C as 16bits of segment
>and 16bits of offset, hence 0x0040:0008 make up the segment:offset
>far pointer. 
>

Both MSC and TURBO C provide a relatively easy method of producing
far pointers without you having to know the internal details of
how the pointers are broken down.  For example, with MSC you can
build the above pointer with:

#include <dos.h>

	FP_SEG(lpts) = 0x0040;
	FP_OFF(lpts) = 0x0008;

I don't know the syntax for TURBO, but they have a "make_far_ptr"
macro which takes a segment and offset and does the bite-twiddling
for you.  Using these macros is much more transparent (i.e. "better
programming style") than hard coding the internal representation
of far pointers into the constant.
-----
	Don Kneller
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