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74AHC is pretty quick 9ns for the 08 and 11.5 for the 138. The real holdup is the time it takes the VDG to release the address bus to the video memory. Maybe if I were doing a re-design I'd use dual port memory there. Vram access time would them be the same as the rom. And allow room to run a couple...

The 65C02 is a relatively new one from WDC, I think their earlier versions were -6 or -8 and may be too slow for 6mhz use - see the math at the end ! The 6847 you sent via Dave happens to be a Motorola MC6847 part, though any of the other manufacturer's versions should operate the same. The 82C55 is...

Here's what's currently on the 6502 system current build, in case someone else wants to build something similar. As the photo's in the first post show, 70% of it is built already, and I've got all the parts needed to complete it. Backplane: 7-15v DC input, on/off switch, 5 and 3.3v regulators, 4 x 6...

:o I didn't think you could push a 6847 to 6MHz.. as they're effectively multiplexed with CPU and only rated at 1MHz ?? :? On 6809 systems they are also tied to a 74LS783 Chip. The 6847 runs off it's own 3.58...mhz clock (NTSC colour burst frequency). The 6502, is one of the newer WDC W65C02S model...

OK, it's not MTX related, or even Z80, but I've got another build running from some of the "extras" I received from Lez, via Dave. Board 1: 6502 CPU, 32k ram, 8k rom, 6mhz clock, and 74 series logic to create a memory map Board 2: 6847 VDG, 82C55 PPI, 8k ram, 74 series buffers to isolate t...

I needed to do something similar for the 6502 board, I was using the BBC basic 3 rom, and the BBC used a 100hz ticker. There wasn't a way to get exactly that from the 4mhz main clock and the /256 pre-scaler setting. (/256 and 156 count =100.2 and /256 and 157 count =99.5 ) So I used /16 and a count ...

I can see one issue, if you look on page 232 of the new manual, it says there's no pre-scaler when the CTC is in counter mode. However you could still use timer mode a large count value to avoid triggering too often, and then do a sub count in the interrupt handler. Possible values 4000000 / 256 = 1...

Sounds like a plan.

Thank you

To add to the list of useful features NEXT without a variable name is allowed Shortened commands when typing ie P. for PRINT Another thing that annoys The editor putting an extra space after DATA I'd hazard a guess that the error "A" was originally "Se.A" and got cropped to save ...

I'm interested!

But first a question. Is there anything in there that's likely to be "new" info ?