Apple II A weird idea...

[The Usotsuki]

Some time ago, I found out about a simple card for an Apple ][ with a TMS9918 and an AY8910.

 

Yes - the video and sound chips from the MSX.

 

I'm making an attempt to figure out how to emulate it knowing its I/O addresses (they're documented on the support disk) and VRAM capacity (16K). If I can get it going, I'm thinking of trying to do some Z80 to 6502 translations from ColecoVision, MSX and SG-1000, and maybe see if the card could be cloned like the Mockingboard.

 

If this could be done...I'm gonna try my damndest.

[JamesD]

I wonder if they even sold 100 of those cards back in the day.
I don't even think they used the overlay mode of the 9918 did they? At least then the sprites and other graphics could be mixed with Apple II graphics.
But then I'm not sure that actually worked on the 9918.

[The Usotsuki]

I'm going to assume "separate monitor" for sanity's sake.

 

I've wired in Marat's 9918 core but I haven't figured out (from Colem) how to get it displaying yet, so there's really no point yet in me trying to plug it into the slot.

[carlsson]

If you get it going, you could start with putting together a Creativision simulator for the Apple II. At least you'd have the CPU and VDP in common, although the Creativision uses SN76489 rather than AY-3-8910. Then again, Colecovision also uses SN sound. MSX uses AY though, as you probably already is well familiar with.

[The Usotsuki]

Well, Marcel de Kogel got ColecoVision running on MSX, with the same difference in sound chips...

[Osgeld]

there's been some talk about using the FPGA version of the TMS on the apple II user group recently, the board you refer to is called the arcade board, video passes from the apple II though it so you only need one display, though its one or the other.

 

I think there's a rom dump of it around somewhere, now its really just a matter of finding a cheap plentiful source of AY chips.

 

course nothing really used it

[The Usotsuki]

Being able to fix that is why I want to emulate it

 

Maybe a source for AY8910s could be Best Electronics? Pretty sure they carry the Yamaha version, or they did when I checked. YM2149, was it?

[JamesD]

If you need an AY chip for prototyping I have a couple tubes of them around here I picked up off of ebay. I'm sure I could part with one cheap.
The main thing is that you'll want to use the same chip you intend to use for production and you might find a better supply of a different variant of the chip than what I have.
Some chips require simpler interface logic.
And I don't know where you live so it might be cheaper to find one local.

Another thing to look at is both chips have been implemented in FPGA's. A small FPGA could mean a much smaller board since you can include some of the other logic.
But that might be a stretch if you aren't familiar with VHDL. If the CFFA cards are any indication you'd need to buffer the I/O lines between the FPGA and Apple connections but you would have the option of expanding on the hardware. A 2nd AY chip in parallel with the 1st one, a later version of the TI video chip once someone posts the VHDL, etc...

[The Usotsuki]

Removing the AY, or moving it to a different address, would be necessary to make full use of a V9938 or V9958...

 

I know all of jack about building hardware - which is why I prefer to "prototype" hardware in software. I can only do rudimentary stuff - that's why the only systems I've made functioning emulators for were the Apple 1, Apple ][, part of an Apple ///, most of a Commodore 3032, and a crude IBM 5160.

 

But I figure - a simple 9918/8910 combination would be a relatively easy way to make something better out of an Apple ][. A library of games already ready to go is a big plus - just think of the difference between the 7800 before and after Pac-Man Plus. I'm planning to take them from the MSX, the Colecovision and the SG-1000, though the necessity of translating the code from Z80 to 6502 will make that quite some work.

[JamesD]

Removing the AY, or moving it to a different address, would be necessary to make full use of a V9938 or V9958...

 

I know all of jack about building hardware - which is why I prefer to "prototype" hardware in software. I can only do rudimentary stuff - that's why the only systems I've made functioning emulators for were the Apple 1, Apple ][, part of an Apple ///, most of a Commodore 3032, and a crude IBM 5160.

 

But I figure - a simple 9918/8910 combination would be a relatively easy way to make something better out of an Apple ][. A library of games already ready to go is a big plus - just think of the difference between the 7800 before and after Pac-Man Plus. I'm planning to take them from the MSX, the Colecovision and the SG-1000, though the necessity of translating the code from Z80 to 6502 will make that quite some work.

Just remember that code is going to grow slightly from the Z80 to 6502. I think code size differed somewhere between 10%-15% for the stuff I ported between the CPUs so make sure there is at least that much RAM available over the size of the Z80 code for the first couple projects. After that you'll have a better idea of difference in code size between the two CPUs for a large project.

[The Usotsuki]

I planned around a 25% increase in size by using Microsoft BASIC as a metric, and figured I'd want to start with Galaxian and Frogger (8K) and Pac-Man (16K) before trying anything bigger. Nothing in my initial plans is bigger than 32K on the Z80.

[The Usotsuki]

I'm having trouble getting the cores to compile, so I'm looking for another solution. Unless, of course, anyone here is familiar with Marat's TMS9918 and AY8910 emulators...

[carlsson]

Of course there are Z80 cards for the Apple ][ as well, so if you have both cards you could try to get them to interact. Eventually you'd get a hardware cousin to MSX, possibly some peripheral chips lacking to make it into full MSX compatibility. It could be an interesting exercise, but someone would point out how much easier it is to use a real MSX computer, Colecovision console etc so unless you find Apple keyboard and joysticks superior to others, the only remaining reason would be "because I can", of course itself a very good reason.

 

But anyway, you have at least 16 unique Creativision games to get to run without doing any Z80 to 6502 conversion, plus a slowly growing homebrew scene.

[The Usotsuki]

Heh, LOL the Softcard.

 

I got the 9918 connected - but it doesn't display anything, and it crashes on exit (prolly got my atexits in the wrong order). Still... I now have the rudiments of the dual head - two windows, keyboard works properly in both of 'em. I'm loath to publicly release anything outside of my usenet posts in comp.emulators.apple2 until I at least get the 9918 functional.

 

So:

 

1. Need to get the 9918 functional.

2. Wire in the AY-8910.

3. Look for games to port... create a code translator if necessary.

 

Well, the Apple sticks are analog, a plus or minus depending on your perspective - should at least be on par with MSX sticks though. Keyboard? Apple ][ keyboards were always great. xD The MSX's biggest advantage was its use of FAT12.

[The Usotsuki]

I put a rough page up at http://buric.co/lemon.htm

 

Lemon is its preliminary name.

[carlsson]

FWIW, the Lemon 64 and Lemon Amiga communities are quite big, so to avoid confusion I'd suggest a different name in the end, perhaps something like Cherimoya unless you think it is too hard to spell. :-)

[The Usotsuki]

Most likely the final name will be "Daplus/AB".

 

I just needed something to name the program while I was working on it.

[The Usotsuki]

There may be hope. I got a fellow emu author I know to try debugging the code and he's managed so far to stop the crashes and get the VDP memory test to pass. Still trying to get a display on the VDP, though.