[v1.1] MECB 1MB ROM Expansion Card

[epaell]

OK, I think I got the data-poll working and have pushed that to my GitHub. I think maybe my error previously was not realising that the LEA operation sometimes affects the Z flag and sometimes not, depending on the register that it is operating on.

[bugeyedcreepy]

Speaking of emulating Consoles though, I've just this morning loaded up the PLD's and ROM and I currently have the really awesome "Attract mode" of the CreatiVision Console's "Sonic Invaders" running on the pixel-sharp TMS9928A RGBS output, complete with it's awesome SN76489 sound effects!

Of course, this isn't "emulation". This is a full recreation of the original hardware config on the MECB bus! With the same chips throughout, as running in an original CreatiVision Console of the early 80's.

This. Is. EPIC!!!

Of course, I still can't play the games, as I still need to make a controller interface to plug into the PIA port on the Mototrola I/O Card.

But, I'm having an awesome time, with lot's of memories flooding back! Not to mention just how good the graphics look, compared to my old memories of a really noisey and artefact-filled RF TV picture, back in the day!

That Is Awesome! maybe another to-do will be an rf modulation card to nostalgically mess up the display on old tv's we all probably still have laying around?

[Editor]

Of course, I still can't play the games, as I still need to make a controller interface to plug into the PIA port on the Mototrola I/O Card.

That Is Awesome! maybe another to-do will be an rf modulation card to nostalgically mess up the display on old tv's we all probably still have laying around?

Well, I probably won't go down that path.

But, the good news is that I'm progressing the controller interface, which has now turned into a PS/2 keyboard and dual joystick PIA interface, that implements the CreatiVision controllers & keyboard.

This involves me diving back into some microcontroller development (but appropriately, I'm using an DIL package 8-bit microcontroller!), which will also have cross-over with what I'd envisioned for an eventual more general PS/2 keyboard etc. MECB Card.
But one thing at at time... too many projects in progress!

[Editor]

OK, I think I got the data-poll working and have pushed that to my GitHub. I think maybe my error previously was not realising that the LEA operation sometimes affects the Z flag and sometimes not, depending on the register that it is operating on.

Nice! Can you elaborate on the LEA issue you came across?

My understanding is that all LEAX and LEAY operations should set/reset the Z flag. But the status flags are untouched by LEAU and LEAS, as thay are stack pointer operations (as opposed to general "register" operations).

[epaell]

Yes, that is exactly the issue I ran into. I was perhaps being a bit lazy and was using the U register to count down and just assumed I could do a BEQ/BNE to check the status.

[Editor]

Yes, that is exactly the issue I ran into. I was perhaps being a bit lazy and was using the U register to count down and just assumed I could do a BEQ/BNE to check the status.

Good to know it was nothing undocumented! I'm still amazed that I had that tid-bit of 6809 information buried in my memory. As I really haven't gone deep on any 6809 coding in a long while. Perhaps this means it'll all come back to me, eventually! LOL

[epaell]

I think I probably made the error, over the decades, of being exposed to the 68000 ... which is such a lovely processor where there are pretty much all the registers behave similarly and completely forgot the peculiarities with the 6809 (and even more so with the 6502 which really is an 8-bit processor).

[epaell]

Just for laughs, I made an MECB 6502 and MECB 6809 emulation in MAME



It emulates the memory, ROM and the ACIA.

MAME also provides a pretty nice debugger:



I'm not sure how practical it is because it doesn't emulate the other MECB I/O but still kind of interesting that it isn't that hard to do this aspect of it.

[epaell]

In case anyone else wants to mess with MAME I've added my updates to GitHub:

https://github.com/epaell/MECB/tree/main/MAME

At least for Linux/Mac computers it is a relatively easy process to get this to work (assuming you can compile MAME in the first place and have all the required tools and dependencies). I've added instructions that worked for me.

I'll probably leave it at that for now since it was more of an academic exercise for me as I always wondered how difficult it was to do something like this in MAME.

[Editor]

I'll probably leave it at that for now since it was more of an academic exercise for me as I always wondered how difficult it was to do something like this in MAME.

Yeah, I will make a point of taking a look at what you've done. Although, similarly, more from a curiosity / interest in how you can do this with MAME.

I'm not a big fan of software emulation, but it would certainly be an interesting and educational exercise to see how MAME facilitates this!