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From: dmt@hocsl.UUCP
Newsgroups: net.micro.pc
Subject: Re: Homebrew Clone Question - (nf)
Message-ID: <146@hocsl.UUCP>
Date: Sat, 21-Jul-84 22:40:07 EDT
Article-I.D.: hocsl.146
Posted: Sat Jul 21 22:40:07 1984
Date-Received: Sun, 22-Jul-84 05:44:00 EDT
References: <6200001@uicsl.UUCP>
Organization: AT&T Information Systems Labs, Holmdel NJ
Lines: 32

REFERENCE:  <6200001@uicsl.UUCP>

Sorry if this is a repost; my UDS modem went "UUUUUUUU....."
in the middle of my last try.

I have built and used the MPX-16 by MicroMint. My "adventures
in compatibility" leave me well qualified to point out the
dangers here. (The MPX isn't quite a clone, more like a
fraternal twin.)

1-	BIOS compatibility is essential. (Necessary but hardly sufficient.)
2-	Be sure the port addresses for all peripherals are identical to IBM.
	You'd be surprised how many IBM programs try to beep the speaker
	on the MPX and then hang (the speaker's on another port).
3-	Be sure all the peripheral chips are the same as the IBM. For
	instance, the MPX serial port is an 8251, not an 8250. This may
	be an improvement, but it's incompatible; terminal emulators like
	the one I use replace the BIOS driver with an interrupt driver
	(that thinks it knows where the port is AND HOW TO HANDLE IT.
	Surprise!)
4-	Which brings us to ....  Be sure all the interrupts (hardware as
	well as software) are the same numbers as the IBM, and on the
	same leads on the 8259 interrupt controller chip. If I had an hour
	now, I'd relate my horror story on that one.
5-	You WON'T get IBM BASICA to run. However, you'll be able to run
	BASICA or GWBASIC for any good compatible (such as the new
	AT&T PC 6300 or the COMPAQ).
6-	Now, as long as the expansion bus is compatible, you've got a
	pretty compatible system.

Good luck.
Dave Tutelman  -  AT&TIS  Holmdel