Saturday, March 24, 2012

Not dead, just resting!

Apologies for the lack of recent updates. Since the last update I've spent a lot of time rewriting the VGA handler so that it better matched Spectrum timings and also had enough clock ticks to create a bordered 512x384 pixl display. This was largely successful but I still could not get a lot of test software to work correctly - in fact most of it was still crashing upon loading. I've come to the conclusion that the soft-core z80 just isn't cutting it.

But I'm not giving up. Not at all! In fact, I've started work on a project similar to ZX Badaloc and Harlequin - a spectrum with an FPGA taking the place of the ULA (and much of the glue logic etc). Most of the work done thus far on the ZX Prism FPGA will be able to be reused. This has the added bonus that, with a minimum of hacking, the FPGA part would be able to be dropped into a "real" spectrum. Another bonus is that I'll be able to do a real edge connector without needing heaps of voltage conversion and FPGA pins...

I'm starting off with the CPU - I've got 10 a Mhz Z80A and a Z80 DMA chip. Once I get my GAL programmer working (or replaced), I'll effectively have a Velesoft Data Gear CPU daughterboard which can be tested on one of my Spectrum 128 machines....

1 comment:

  1. Which softcore Z80 are you using? The latest T80? I've found that's pretty bullet-proof in a lot of projects, except for the Gameboy which is documented as being "experimental" in the core...

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