Could an AVR be used as a cart rom?

[cbmeeks]

So, say I find an AVR with a high pin count and lots of FLASH. Could that be used as a ROM for a cart?

 

Or would you need glue logic in between like a PLD?

[roland p]

The Harmony uses a micro controller so it works for the 2600 (1.19MHz, ColecoVision runs at 3.58MHz.).

Edited April 17, 2015 by roland p

[cbmeeks]

Ah good point. BitBanging at that speed would be an issue for an AVR.

[+GroovyBee]

I use an AVR in my Bee3 cart design for the Intellivision :-

 

http://atariage.com/forums/topic/225566-bee3-its-alive/

 

However, the Intellivision has a multiplexed address/data bus and takes several clock cycles in each bus phase. The latest design does have extra stuff around the AVR to make the CPUs life a bit easier.

[cbmeeks]

That's pretty awesome.

 

I was thinking of trying to clock a Z80 with a propeller along with using the prop as RAM/ROM.

 

I believe the prop can easily handle the 3-4MHz. :-)

[+GroovyBee]

As a first thought, it might be possible to do something with an XMEGA at 32MHz and make use of the Z80's T-states. However, without investigating the problem in much more detail its just a theory. The first "gotcha" to overcome would be detecting the DRAM refresh cycles.

 

Edit: You'd also need 5v to 3v level conversion as well (if you go down the XMEGA route). That adds additional cost and PCB routing which might be a factor.

Edited April 26, 2015 by GroovyBee

[cbmeeks]

Yeah, I will have the same issue with the propeller. It's 3.3v as well. Would be much easier for us retro nuts if everyone went back to 5V. LOL

[+GroovyBee]

You could use a 5v tolerant CPU like the LPCxxxx ARM series from NXP. At 60MHz you should be able to offer on cart ROM and RAM and maybe other features too e.g. E2PROM for game data saves. NXP's Cortex range would be a good start.

[cbmeeks]

That's a good idea but I wanted to stick with the prop because I plan on using the other cogs (cores) for other things like video and audio.

 

Plus, I already have some level shifters.

[+GroovyBee]

That's a good idea but I wanted to stick with the prop because I plan on using the other cogs (cores) for other things like video and audio.

I don't think the standard CV cart port has audio/video in.

[cbmeeks]

It doesn't. What I planned on doing was using the prop to copy the cart to memory and then drive the CPU from external memory.

[+GroovyBee]

So its some kind of cart/F18A combo project?

[cbmeeks]

Can't afford an F18A. :-)

 

But it's along those lines. The propeller (http://forums.parallax.com/showthread.php/138254-TEXAS-INSTRUMENTS-TMS9918-9928-VDP-Emulation-on-Propeller?highlight=tms9928) can output video using software. Plus, it can emulate the SN76489 sound chip (among others) at the same time.

 

It's an experiment, really. What I want to do is emulate a ColecoVision using a *real* Z80 connected to the propeller. The propeller (prop) would then stand in as RAM/ROM for the Z80 and emulate the audio/video of the CV. Like a hybrid.

 

That's the dream, anyway.

[+GroovyBee]

That kind of project is well beyond the realms of a simple AVR/LPC device.

[cbmeeks]

Yep. Hence, the propeller. :-)

 

My first idea was to simply create my own "multi-cart" but using the AVR to act as the ROM ( the original point of this post). But the more I get into it, the more I want my own hybrid CV.

 

I can't ever do anything simple. lol

[+GroovyBee]

In that case, just put a cart connector on the design and be done .