keller@uicsl.UUCP (07/20/84)
#N:uicsl:6200001:000:914 uicsl!keller Jul 19 17:21:00 1984 I am considering building an IBM-PC compatable from the Display Telecommunications Corp. MEGA-BOARD. If you have done this I would love to hear from you! If you haven't built one of these but you know about the IBM-PC and what might be difficult to duplicate I'd like to hear from you too. The MEGA-BOARD is advertised in the latest BYTE (July '84) on page 449. It is a very plain board that elaborates just a little on the IBM board. It seems to me that the secret to building a successful clone is in the ROMs. DTC says that they have a fully compatable BIOS ROM that allows you to boot MS-DOS. I'm wondering if that is all you need in the way of ROM code (just a BIOS). Now the IBM design may suck, but you can get work done on it and with a production of one every 7 seconds you know that they are going to be around for a while. Wouldn't you like to take advantage of good deals like Turbo Pascal? -Shaun
dmt@hocsl.UUCP (07/22/84)
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