8086 uP Require

The CPUs he tries seem to be running programs fine, it's the display screen he's complaining about. But I think your intuition might be right on target, with respect to the shortened timing requirements. It's not necessarily access speed, since that was pretty relaxed for the 8086 family. My concern was with the data bus hold-time issue.

. CLK ___ ___ ___ ___ ___ ___ . ___/ \\____/ \\____/ \\____/ \\____/ \\____/ \\__ . ________ ___________________________________ . ---X________X___________________________________X--- . ADDRESS DATA OUT | . TWHDX . ________________ |___________ . WR* \\________________________________/

I'm thinking that the TWHDX data-hold time, which can be as short as 20 to 40ns for the 8086-1, can get designs into trouble. Look at the time scales here. Faster memory might get them out of this trouble. Of course, the new fast memory may not be pin compatible. Life is not easy.

Unlike some of the right-wing advocates here on s.e.d., I'm not one to see things in black and white. While faster ram memory might help solve WayneL's problem, it's also possible slower memory might be the solution. That's because some slow memory ICs will store the data-bus contents 50's of nanoseconds before the end of the WR* strobe pulse. Slow memory tends to have a longer data-change setup time. In some designs, slow RAM available when the design was tested might have led to an unworthy confidence. Later on, new, faster RAM can destroy the design's safety margins, and render late production a fragile product. As in so many issues, the precise details determine the exact answer.

Modern designs could potentially suffer from these same issues, but many employ a power solution, that wasn't available in the old days.

It would be great if it would solve his problem!

Oh, BARF! Gray is for political hacks... black and white is for engineering.

Good design does NOT rely on set-up-and-hold times as part of the system timing.

...Jim Thompson

Agreed. We're talking about designs > 20 years ago, made with limited resources. Unfortunately many such designs did not bite the bullet and add the extra fast buffer chips necessary for proper safe synchronous designs. I did many bullet-proof synchronous designs in the mid 70s. So I'd say, while there may not have been sufficient excuse for taking the cheap way out in the mid 80s, I know it was commonplace. If you look at Intel and other app notes of the day, you'll see it was common.

If it doesn't, I wonder how an NEC V30 would fare ?

Graham

I recall doing some work for a marine radar company that made its own

One in 10 or so simply never worked they said.

Graham

Weren't the NEC chips upgrades for the 8088? I know the V20 was.

As the V20 was an 8088 replacement, so the V30 was an 8086 replacement:

// Christian Brunschen

Thanks, I had never used the V30 and I couldn't remember the V30 specs.

They were indeed. That means some timings are likely to be different but that might work in the OP's favour since we don't know the reason for his display issue.

Graham

No, it means it's useless in an 8086 socket - they have different data busses. But I had thought that the V30 was just a hot V20, and the V40 was the 16-bit one, or am I thinking 286?

Thanks, Rich

The V30 is a drop-in replacement for an 8086. I fited one in my Amstrad PC of old. It does the sums faster !

Graham

Did you find an 8086-1 yet? If not, I just found one I could send, although I can't guarantee that it works.

Glen

On Tue, 24 Jan 2006 22:33:21 GMT, Rich Grise sprachen:

IIRC, from reading a useless old IBM PC handbook (written in '81ish and very useful, but this was in about '94. Stupid library, stupid council / government f****ng budget cuts to give tax bribes to their rich mates etc etc etc).

But any, IIRC, it was the address bus that also doubled (was multiplexed) with the data bus.

The 8086 had it's 20 address lines, the lower 16 of which were D15..D0 . On the 8088 only the bottom 8 addr lines were D7...D0. Pin-wise there's no saving, IIRC there's some pin on the chip that tells you whether the bus has address or data on it.

The IO was obviously multiplexed into the memory range, same as the Z80, same as practically every CPU I can think of. Don't even Pentiums use the same addr/data and an IORQ/MEMRQ pin (or possibly 40 of each to handle the current demands. Next year's big computer comes with optional PSU / arc welder)?

Anyway... it was really a good idea. Save a damn fortune on excess glue and RAM, use existing, popular support chips, and still enjoy

Actually a lot of early 80s arcade games used an 8086. Tho Bubble Bobble, in about 1985, used 3 Z80s. At the time, as a product of price and power, it was a brilliant idea. Just god-awful to program. Fortunately we're just about over that legacy.

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if love is a drug, then, ideally, it's a healing, healthful drug... it's kind of like prozac is supposed to work (without the sexual side effects and long-term damage to the brain and psyche)

Thanks Glen, Found one. Cheers