Path: utzoo!attcan!uunet!clyde.concordia.ca!jarvis.csri.toronto.edu!utgpu!watserv1!watcgl!electro!ignac
From: ignac@electro.UUCP (Ignac Kolenko)
Newsgroups: comp.sys.atari.st
Subject: Re: Cartridge port
Message-ID: <1242@electro.UUCP>
Date: 21 Dec 89 18:31:52 GMT
References: <21556@uflorida.cis.ufl.EDU>
Reply-To: ignac@electro.UUCP (Ignac Kolenko)
Distribution: na
Organization: Electrohome Ltd., Kitchener, ON
Lines: 34

In article <21556@uflorida.cis.ufl.EDU> rs0@beach.cis.ufl.edu (Bob Slaughter) writes:
>I am looking for info on using the cartridge port as an I/O port.  I
>need D0-D8, A0-A15, and how the port does read vs. write (MEMR* and
>MEMW* lines line an InTel, or R/W* with clock strobe ala 6502).  The
>docs that come with the ST have the pinouts for most of these, but the
>port direction control is not clear at all from their diagram.  If you
>have to know, this is related to C/MRI project from Model Railroader
>(Computer/Model Railroad Interface), as now reprinted in Bruce Chubb's
>"How to Build a Universal Computer Interface".  I know the port can be
>written to, otherwise how do you set all those nice clock carts? :)  I



nope. its a read only port. hence the Atari name: ROM Cartridge Port. :-)

but you can develop ways of tricking the cartridge port to allow you to
do a write, which is basically how the clock cards are set on the ST. an
easy way of doing this is decoding a read from any address in, say the
$FA0000 range to be a 16 bit write to the cart port. thus, whatever address
with $FA in the upper 8 address bits can be turned into a write pulse,
(ROM4 is the strobe that's generated by the mmu i think) and use the
lower 16 bits of the address bus as the fudged data bus. not too pretty but
it works great.

(the addresses are off the top of my head, and may be wrong. mebbe someone
else can verify for me)



-- 
=====Ignac A. Kolenko (The Ig)           watmath!watcgl!electro!ignac=====
     co-author of QuickST, and the entire line of Quick Shareware!!!!
       "I don't care if I don't win, 'cause I don't care if I fail"
             from 'Youth Of Today' by SUBURBAN DISTORTION