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- Path: sparky!uunet!utcsri!torn!utzoo!censor!isgtec!bmw
- From: bmw@isgtec.com (Bruce M. Walker)
- Newsgroups: sci.electronics
- Subject: Re: Disk drive fails when pc card plugged, why?
- Message-ID: <3640@isgtec.isgtec.com>
- Date: 9 Nov 92 19:03:44 GMT
- References: <1992Nov6.142220.19884@cactus.org> <40712@sdcc12.ucsd.edu>
- Sender: root@isgtec.com
- Distribution: usa
- Organization: ISG Technologies Inc., Mississauga Ontario
- Lines: 34
-
- In article <40712@sdcc12.ucsd.edu> vwass@sdcc13.ucsd.edu (Vincent Wass) writes:
- > I am having trouble with a computer interface project. I'm trying
- > to decode addresses on the bus for my own plug-in wire-wrap card.
- > So I used a 74ls688 compare chip to
- > decode address lines A2 to A9, and then I wired A0 and A1 to an 8255
- > chip. I've wired the address to be 300hex. I've also tried 280hex,
- > but I had the same problem [, disk-related errors].
-
- Here are some things to watch out for:
-
- a) keep all wires to the card edge fingers (ie the bus) *really* short.
- The best way to ensure this is to place the sockets for the bus
- buffers right along the closest row of holes to the fingers.
- Do not exceed two inches. Really.
-
- b) buffer *all* signals with a single LS TTL load. The IBM "spec" says two
- LS loads, but some buses are longer and some cards cheat. A fully loaded
- system may become overloaded when you add your board.
-
- This also means you should buffer the lines going to the 8255; stick
- in an LS244 and ground the /enable (always on) and buffer A0, A1,
- /RD, /WR, etc. A MOS device like the 8255 represents a capacitive load
- that slows the risetime of those bus signals.
-
- c) use a utility to map out what i/o devices are in your system. 0x300
- and 0x280 are likely OK, but some older PCs and XTs used 0x300 for the
- time-of-day clock.
-
- Have fun!
-
- --
- "The path of my life is strewn with cowpats from the devils' own herd."
- -- Edmund Blackadder II
- bmw@isgtec.com [ ...!uunet.ca!isgtec!bmw ] Bruce Walker
-