MZ-80A / MZ-80K extra RAM
Re: MZ-80A / MZ-80K extra RAM
If you want faster video ram access you can always modify the hardware to use the HBL instead of the VBL you get 25 HBL / 1 VBL.
On the MZ80K this effected the keyboard input routine and you got about 20 characters per keyboard press not very helpful.
On the MZ80K this effected the keyboard input routine and you got about 20 characters per keyboard press not very helpful.
Re: MZ-80A / MZ-80K extra RAM
There is use in the extra VRAM. I use the second page in conjunction with an interrupt to swap between VRAM pages on my 80A to create new (non Sharp) graphic characters and special fx.
Re: MZ-80A / MZ-80K extra RAM
It is just for MZ-80 A which has the hardware scrolling so the swapping is just a matter of setting the page address every line at most. Scrolling hardware is done by accessing the address between $E200-$E2FF (one byte is 8-character unit, so the next line is 40/8 further, that is $E200+5*N where N is the line (between 0 and 50).
Re: MZ-80A / MZ-80K extra RAM
Re: MZ-80A / MZ-80K extra RAM
Although that isn't the interrupt part but shows how to swap between pages of VRAM. Is this actually not available on the MZ-700 ?!
Re: MZ-80A / MZ-80K extra RAM
Nope, again MZ-700 is not retrocompatible with MZ-80 A but with MZ-80 K. There is no successor to MZ-80 A.
Re: MZ-80A / MZ-80K extra RAM
And while I may be attempted to add that missing feature which seems inherited from MZ-80 B (yeah MZ-80 A nd B share the same video circuit at some point), I'm not sure it may be easy to do so with an hardware add-on without butchering the mother-board.
Re: MZ-80A / MZ-80K extra RAM
Here is the retrocompatibility chain in my opinion:
Code: Select all
MZ-80K ___ MZ-80C ____ MZ-1200
\__ MZ-80A
\_ MZ-700 ___ MZ-1500
\_ MZ-800
Re: MZ-80A / MZ-80K extra RAM
Thanks, that's a good diagram! It'd be nice to expand that into the other MZs. Because, for instance, I don't really understand what the MZ-2200 is, and some of the others.