HBLANK (MZ-80A)

User avatar
mz-80a
Posts: 361
Joined: Thu Jan 25, 2018 10:46 am
Location: Devon, UK
Contact:

Re: HBLANK (MZ-80A)

Post by mz-80a »

So POKEing to the screen on the 80K creates snow effect. POKEing to the screen on the 80A does not. Just need to know why not. Or is that what you mean by "Printing to the screen uses the V-HBlank signal" ?
MZ-80A Secrets
https://mz-80a.com/

Sharpworks (Sharp MZ homebrew)
http://mz-sharpworks.co.uk/
hlide
Posts: 667
Joined: Thu Jan 25, 2018 9:31 pm

Re: HBLANK (MZ-80A)

Post by hlide »

Usually it is up to the peripheral card to set the /EXWAIT pin, not the GAL. MZ-700 LSI outputs /WAIT but not for $F000-$FFFF so I don't think it is the case for MZ-80A too. The /EXWAIT and /WAIT should have a circuit so it can feed the Z80. But the actual schematics show nothing about the circuit and /WAIT label is just connected to Z80 with no more available information. There is a circuit mixing BLNK and CSD to allow for Z80 to access VRAM but that's just a part of the whole video circuit. Only the GAL can tell to Z80 if Z80 can access to VRAM without conflicting the video circuit reading VRAM. MZ-80 K has conflict (that's why we have snow effect). Running the same program with snow effect on a MZ-80 A has NO snow effect regardless the drawing synchronization upon VSYNC.

Again I only hope to have a working MZ-80 A to use my LA5032 and capture interesting signals but I'm not in a situation I can afford that for a long moment.
hlide
Posts: 667
Joined: Thu Jan 25, 2018 9:31 pm

Re: HBLANK (MZ-80A)

Post by hlide »

And yes, on MZ-80 K schematics, Z80 /WAIT is directly connected to 5V through a pullup. At least, it is clear. For MZ-80 A, just a label /WAIT. It cannot be floating so it lacks at least a circuit mixing /EXWAIT to connect Z80 /WAIT.
User avatar
mz-80a
Posts: 361
Joined: Thu Jan 25, 2018 10:46 am
Location: Devon, UK
Contact:

Re: HBLANK (MZ-80A)

Post by mz-80a »

We really need some serious in-depth analysis of the MZ-80A :) It's strange that there are so many 80A schematics but not precisely what we want to see.

Hlide, I would like to send you another MZ-80A (I know the first one didn't arrive in very good condition at all - I was fairly horrified by how the parcel had been treated in fact!). It does have the usual 'collapsed video' problem. So, either I have to fix that somehow (with some help from folks over here) or you would have to fix it. To send it, I would make sure it was packed in a way that it could not be damaged again.
MZ-80A Secrets
https://mz-80a.com/

Sharpworks (Sharp MZ homebrew)
http://mz-sharpworks.co.uk/
hlide
Posts: 667
Joined: Thu Jan 25, 2018 9:31 pm

Re: HBLANK (MZ-80A)

Post by hlide »

Let us see later, my actual situation is not propice for doing so.
User avatar
mz-80a
Posts: 361
Joined: Thu Jan 25, 2018 10:46 am
Location: Devon, UK
Contact:

Re: HBLANK (MZ-80A)

Post by mz-80a »

OK, well the offer is there.
I think I'll try and get it fixed first.
MZ-80A Secrets
https://mz-80a.com/

Sharpworks (Sharp MZ homebrew)
http://mz-sharpworks.co.uk/
Post Reply