[v2.0] MECB 68008 CPU Card

[epaell]

Whenever I see a nice looking white marker pen I'll buy it. I use them for adding clear markings for connector pin one and such on boards (top and bottom), usb connectors too so you know which way to plug them without the usual trial and error fumblings. I wish I could say it stops me making stupid mistakes.

LOL, I don't believe there is ever a right way to plug a usb connector in on the first attempt - it always seems to be in some weird quantum state!

[epaell]

Some more progress with testing. I've translated all the OLED routines for 68000 use. I also ported across the Motorola fast floating point routines and wrote handling for the Corsham SD card interface. While I don't have any fancy access to it yet I can at least get a directory of files and open, read and write to files. The plus of this is that I can now combine it with the FLASH ROM routines I wrote to allow firmware updates to be easily written to the expansion ROM via an image on the SD card (no more unplugging and plugging of the ROM device. I tested this by creating a library with all of the routines (including the font definition) and added them to the FLASH ROM so I only need to make calls to the ROM rather than having to download large chunks via S19 format. Proof of concept was writing a simple surface drawing plot using the math library (all using floating point arithmetic) and then plotting with the OLED library. I'd have to say that the Motorola FFP library is really super slick and fun to work with.

I was also chatting to my brother about the odd handling of the I/O signals in the 68008 manual and he said that he never use that in his designs (and also didn't understand why it was needed). So I removed the 74LS73 suggested by the manual, added a minor bodge wire to move some signals over and reprogrammed the GAL to invert the active state of one of the signals and confirmed that this does indeed work absolutely fine.

[Editor]

Some more progress...

That’s all really exciting stuff! Awesome progress.

One thing about the OLED Display (that has provided a good outcome with my DREAM project), is the performance.

The original DREAM designer was really impressed with the speed I’m getting out of the OLED controller. e.g. When playing DREAM Invaders.

He had experience with using some older LCD controllers, and noted that he always had a performance / update speed issue when trying to create anything requiring fast graphics updates.

So, overall, I’m very happy with the performance of the MECB OLED Display Card. Noting also, that only the parallel interfaced modules (like I use), allow reading of the internal display buffer (the serial interfaced panels only allow write access).

So, although a relatively small screen, the OLED Display Card actually makes a really great little retro display. Especially when you consider that 128x64 chunky retro graphics doesn't really need a "big" screen.

[epaell]

I'd have to admit that I've mostly been concentrating on functionality and not so much performance so my code is probably horribly inefficient (particularly as I warm myself up with 68000 programming again and also try to make these routines as easy to use as possible). Having said that, I'm really loving the OLED module as it is nicely self-contained and simple to use ... as opposed to my other display which just adds a whole lot more cabling and conversion boxes to get it running in the small workspace I have available.

[Editor]

I think I’m finally finished with my v2.0 take on the MECB 68008 CPU card.

It seems to have been an “over the holidays” project, with me spending too much time tweaking PCB layout and routing!

My main challenge seems to be that I get so caught-up in the hardware design aspect, that I don’t get the time (that I want), to play with the software.

Actually, over the beginning of January I seem to now have designed two new MECB CPU Cards. Something just keeps me coming back to KiCAD! LOL

So, I thought I’d share my (final?) 68008 v2.0 PCB design here first (perhaps also to encourage me to stop tweaking it!).

Here it is (I hope you like how it’s turned out):

[epaell]

That looks fantastic - I'm impressed that you were able to squeeze all that on the one board ... not to mention leave so much space for useful labelling ... and an additional 5x2 plug - is that for testing or does it provide something out of additional PLD pins?

[Editor]

That looks fantastic - I'm impressed that you were able to squeeze all that on the one board ... not to mention leave so much space for useful labelling ... and an additional 5x2 plug - is that for testing or does it provide something out of additional PLD pins?

Thanks for the compliments! Much appreciated.

The 5x2 plug is the JTAG connector for in-circuit programming of the CPLD. The ATF1502 uses a JTAG interface for programming, so you do need a JTAG programmer. I got the official Microchip ATDH1150USB programmer (but 3rd party JTAG programmers are also available).

BUT, the good news is that if you get a pre-programmed CPLD, then you won't even need to solder in this connector. Simply because, the CPLD for the 68008 card will probably not need to be re-programmed, given the large memory space and likely no need to ever change the memory map.

i.e. With 2MB on-board, and MECB space (mreq) to add a further 1MB of memory (RAM or ROM), there's plenty of space to just leave the iorq allocation consuming the whole remaining 3xxxxxx memory space.

As you'll note, I've basically used the same memory map that you implemented. So any code you've already written should just run on the v2.0 card, without any change. That's also why I went as far as labelling the Memory Map on the PCB silkscreen.

[Editor]

FYI. I've now updated the original topic post and noted the topic as as [v2.0] (instead of [P]lanned), along with a link to the now published Blog.

EDIT: I've also now added a new Software forum: 68008 / 68000
For the purpose of Software related discussion for the 68K ISA.