Path: utzoo!attcan!uunet!husc6!rutgers!mcnc!rti!sunpix!matthew
From: matthew@sunpix.UUCP ( Sun NCAA)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Interfacing to the PC bus
Message-ID: <275@greens.UUCP>
Date: 17 Nov 88 17:50:26 GMT
References: <1717@questar.QUESTAR.MN.ORG> <4617@bsu-cs.UUCP> <90@usl-pc.usl.edu> <17932@shemp.CS.UCLA.EDU>
Organization: Sun Microsystems, Research Triangle Park, NC
Lines: 49

In article <17932@shemp.CS.UCLA.EDU>, jsin@maui.cs.ucla.edu (Jonghoon Sin) writes:
> I'm posting this for a friend:
> 
>   I've built some hardware that interfaces to the PC through three 8 bit
> I/O ports.  I've used a 8255 with a couple of other TTL/LS chips as glue.
> My questions are:
> 
>   1.  In a minimal PC configuration (256K RAM, 1 floppy/controller,
>       monochrome card) what port addresses are typically unoccupied?
>       Is the area 03C0 to 03CF safe to use?
> 
>   2.  I'm finding that the IOW' line is asserted about
>       every 15us.  Is this normal?  What's the PC doing?
> 
>   I should mention that I'm using a 4.77/8Mhz Taiwanese clone and
>   not a True Blue PC.

The IBM Personal Computer Hardware Reference Library back to the rescue again.

The writer of this article, and of another one I recently read, should get some
useful info out of this post. Below is a copy of the I/O address map on page
2-23 of the above manual (notice, that due to incomplete decoding, that I/O
space within the range $000 thru $0FF is consumed by the motherboard).


Hex-Range  9  8  7  6  5  4  3  2  1  0    device
----------------------------------------------------------
 00-0f     0  0  0  0  0  Z A3 A2 A1 A0    DMA Chip 8237-2
 20-21     0  0  0  0  1  Z  Z  Z  Z A0    INTERUPT 8259A
 40-43     0  0  0  1  0  Z  Z  Z A1 A0    TIMER 8253-5
 60-63     0  0  0  1  1  Z  Z  Z A1 A0    PPI 8255A-5
 80-83     0  0  1  0  0  Z  Z  Z A1 A0    DMA PAGE REGS
 AX        0  0  1  0  1  Z  Z  Z  Z  Z    NMI MASK REG
 CX        0  0  1  1  0  Z  Z  Z  Z  Z    RESERVED
 EX        0  0  1  1  1  Z  Z  Z  Z  Z    RESERVED
----------------------------------------------------------
200-20F    1  0  0  0  0  0 A3 A2 A1 A0    GAME I/O ADAPTER
278-27F    1  0  0  1  1  1  1 A2 A1 A0    RESERVED
2F8-2FF    1  0  1  1  1  1  1 A2 A1 A0    RESERVED
378-37F    1  1  0  1  1  1  1  Z A1 A0    PARALLEL PRTR PORT
3B0-3BF    1  1  1  0  1  1 A3 A2 A1 A0    IBM MONOCHROMATIC DISPLAY/
                                           PARALLEL PRINTER ADAPTER
3D0-3DF    1  1  1  1  0  1 A3 A2 A1 A0    COLOR GRAPHICS ADAPTER
3F8-3FF    1  1  1  1  1  1  1 A2 A1 A0    TP RS-232-C CD

-- 
Matthew Lee Stier     (919) 469-8300|
Sun Microsystems ---  RTP, NC  27560|          "Wisconsin   Escapee"
uucp: {sun, rti}!sunpix!matthew     |