Looping access from 68K and Z80

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Miquel
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Re: Looping access from 68K and Z80

Post by Miquel » Mon Nov 19, 2018 6:23 pm

Eke wrote:
Sat Nov 17, 2018 5:25 pm
The reason access to VDP from 68k through Z80 address locks the system is likely due to the fact Bus Arbiter requests 68k bus in case of access to 68k bus from Z80 bus master but since 68k is the initiator of the access and is waiting for !DTACK to complete the bus cycle, 68k bus access is never granted.
I’m struggling following all this, but following the explanation you just give if 68K->Z80->68K was access thought buses it will lock the system at any access not only on VPD access, correct?

Eke
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Re: Looping access from 68K and Z80

Post by Eke » Mon Nov 19, 2018 8:25 pm

if 68K->Z80->68K was access thought buses it will lock the system at any access not only on VPD access, correct?
As said previously, ZA15 is forced low when 68k is accessing Z80 bus so it's not possible to access 68k bank in Z80 memory map upper area ($8000-$FFFF) from 68k since it becomes a mirror of lower area ($0000-$7FFF) and therefore only banked VDP access (between $7F00-$7F1F) are possible.

Enforcer
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Re: Looping access from 68K and Z80

Post by Enforcer » Tue Nov 20, 2018 6:41 am

My breakout boards cam it but sadly the pads for the pins on the chip were just a tad too short. New boards ordered but with the US holiday coming up it’ll be 10-14 days before I get them back. In the meantime, I found a semiconductor seller that had some genesis chips in stock so I picked up a couple 5308s, 5309s and 5313. I’ll use them for figuring out their logic and I may send some off to get recapped and photographed if I can find a place that’ll do it cheap enough. Otherwise I may take a stab at it.

Chilly Willy
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Re: Looping access from 68K and Z80

Post by Chilly Willy » Tue Nov 20, 2018 3:01 pm

Who do you buy you Genesis chips from? I'd love to get a few for my own purposes.

Sik
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Re: Looping access from 68K and Z80

Post by Sik » Tue Nov 20, 2018 3:16 pm

There are a bunch of brokers who seem to sell just about everything they can get their hands on without thinking much about it (spare chips salvaged from dead consoles, spares that were left in warehouses, etc.). I remember running into brokers some years ago and a couple of Japanese people I know decided to buy a VDP because why not.

And yeah, would be interesting to know who's selling that stuff right now.
Sik is pronounced as "seek", not as "sick".

Enforcer
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Re: Looping access from 68K and Z80

Post by Enforcer » Tue Nov 20, 2018 3:56 pm

https://www.questcomp.com Is who I went through since they didn’t require a quoting process. The other one I’ve seen was New York Semi.

Mask of Destiny
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Re: Looping access from 68K and Z80

Post by Mask of Destiny » Tue Nov 20, 2018 7:30 pm

Enforcer wrote:
Tue Nov 20, 2018 6:41 am
My breakout boards cam it but sadly the pads for the pins on the chip were just a tad too short. New boards ordered but with the US holiday coming up it’ll be 10-14 days before I get them back. In the meantime, I found a semiconductor seller that had some genesis chips in stock so I picked up a couple 5308s, 5309s and 5313. I’ll use them for figuring out their logic and I may send some off to get recapped and photographed if I can find a place that’ll do it cheap enough. Otherwise I may take a stab at it.
FYI: 5313 and 5313A have been decapped already. Low res of both are here. High res of the 5313 is linked from here. There's a small group of us that started the process of reversing it, but it's' currently paused until we work out some tooling issues.

Enforcer
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Re: Looping access from 68K and Z80

Post by Enforcer » Tue Nov 27, 2018 4:54 am

That’s pretty cool about reversing the 5313. How does one get involved with that? Also, I got all my chips from quest components. They all look to be in perfect shape. I was surprised at how well packaged it all came.

Chilly Willy
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Re: Looping access from 68K and Z80

Post by Chilly Willy » Tue Nov 27, 2018 1:34 pm

How long ago was that? Can't seem to find any at Quest at all.

Enforcer
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Re: Looping access from 68K and Z80

Post by Enforcer » Tue Nov 27, 2018 2:07 pm

Ordered last week and got them last night. https://www.questcomp.com/part/4/315-5313A-01/432898428

Chilly Willy
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Re: Looping access from 68K and Z80

Post by Chilly Willy » Thu Nov 29, 2018 7:33 pm

Thanks for the link. Their search really sucks. I couldn't get a single hit from any form of the part number.

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