TechTools Archives: Re: RASTER: FW: Using 8080 pod on Midway 808

From: Alex Yeckley <ayeckley_at_sierralobo.com>
Date: Tue Feb 19 2013 - 09:03:00 EST

There's nothing about the Midway 8080 board design that prevents the
9010/8080 pod from performing successful RAM tests (short or long) or
running the UUT with a "standard" speed 8080 (even with its interleaved RAM
scheme). We do it literally almost every day. We have seen a failure of a
6502 pod such that the address driver line was "weak" and couldn't always
drive successfully drive the pin above the TTL threshold. That same pod
would pass its own self test, presumably because the loopback inputs of the
pod have higher impedance than the target board address lines. Perhaps
something like that is happening here?

Alex Yeckley
Senior Electro-Mechanical Engineer
Sierra Lobo, Inc.
11401 Hoover Road
Milan, Ohio 44846

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-----Original Message-----
From: techtoolslist-bounces@flippers.com
[mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson
Sent: Monday, February 18, 2013 11:13 PM
To: techtoolslist@flippers.com
Subject: Re: [Techtoolslist] RASTER: FW: Using 8080 pod on Midway 8080
boards (Space Invaders)

David Shoemaker wrote:
> The pod has a -1 CPU in it which should be good to 3 mhz the board is a
> straight 8080a which should be 2mhz. But I tried it with the CPU from the
> board just for completeness. No improvement. And the pod cpu works fine
in
> game.
>
> I have one board that will at least start up partially with the pod, but
two
> others that just error on Run UUT.
>
> It is really inconsistent. I think the way the memory system works the
fluke
> ram test will never work (strange timing and sync to get the game board
> rotation stuff to coordinate access to ram).
>
> I have two of these pods, both use the flat ribbon. I tried subbing a
> twisted ribbon from an 8085 pod but the pod fails self test (I suspect the
> ground lead is mucking with something).
>
>

I was testing an 8080 board only last year, but didn't get it booting,
so it is sitting waiting for me to take another go. I can't recall doing
the "Run" on any of the 8080 boards recently so haven't any better ideas
at the moment...

Perhaps someone else here has a suggestion?

John :-#)#
> -----Original Message-----
> From: techtoolslist-bounces@flippers.com
> [mailto:techtoolslist-bounces@flippers.com] On Behalf Of John Robertson
> Sent: Sunday, February 17, 2013 7:23 PM
> To: techtoolslist@flippers.com
> Subject: Re: [Techtoolslist] RASTER: FW: Using 8080 pod on Midway 8080
> boards (Space Invaders)
>
> David Shoemaker wrote:
>
>> So my mails to tech tools don't appear to be getting through. But this
>> is a raster game so I will cross the stream.
>>
>>
>>
>> *From:* David Shoemaker [mailto:davids@oz.net]
>> *Sent:* Saturday, February 16, 2013 12:20 AM
>> *To:* 'Technical Tools Mail List'
>> *Subject:* Using 8080 pod on Midway 8080 boards?
>>
>>
>>
>> I have a fully working space invaders board which when I hook the pod
>> up to and do Run UUT doesn't, it starts up and crashes.
>>
>>
>>
>> Pod passes self test.
>>
>>
>>
>> Anyone ever done this?
>>
>>
>>
>> David
>>
>>
> Try a faster 8080 CPU in the pod, or try substituting the 8080 from the
game
> in place of the pod CPU. It is possible the CPU is bad or slower than the
> system can handle.
>
> Do you have the flat ribbon cable from the pod to the CPU socket or the
> twisted pair cable? The twisted pair cable handles noise better and will
> work in situations when the simple flat cable won't, plus it can be longer
> as a result.
>
> David, I have no idea why this did not show up in TTL - you are subscribed
> under the same email address as you posted here. I haven't seen any
bounces
> for your email address.
>
> John :-#)#
>
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Re: RASTER: FW: Using 8080 pod on Midway 8080 boards (Space Invaders)