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Re: Looping access from 68K and Z80
Posted: Mon Nov 19, 2018 6:23 pm
by Miquel
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?
Re: Looping access from 68K and Z80
Posted: Mon Nov 19, 2018 8:25 pm
by Eke
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.
Re: Looping access from 68K and Z80
Posted: Tue Nov 20, 2018 6:41 am
by Enforcer
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.
Re: Looping access from 68K and Z80
Posted: Tue Nov 20, 2018 3:01 pm
by Chilly Willy
Who do you buy you Genesis chips from? I'd love to get a few for my own purposes.
Re: Looping access from 68K and Z80
Posted: Tue Nov 20, 2018 3:16 pm
by Sik
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.
Re: Looping access from 68K and Z80
Posted: Tue Nov 20, 2018 3:56 pm
by Enforcer
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.
Re: Looping access from 68K and Z80
Posted: Tue Nov 20, 2018 7:30 pm
by Mask of Destiny
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.
Re: Looping access from 68K and Z80
Posted: Tue Nov 27, 2018 4:54 am
by Enforcer
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.
Re: Looping access from 68K and Z80
Posted: Tue Nov 27, 2018 1:34 pm
by Chilly Willy
How long ago was that? Can't seem to find any at Quest at all.
Re: Looping access from 68K and Z80
Posted: Tue Nov 27, 2018 2:07 pm
by Enforcer
Re: Looping access from 68K and Z80
Posted: Thu Nov 29, 2018 7:33 pm
by Chilly Willy
Thanks for the link. Their search really sucks. I couldn't get a single hit from any form of the part number.