Great feedback as always, I think I got tripped up again by Grants design being NMOS based (again). SYNC, I have no answer for, I knew the answer and still wired it up wrong.

So am no longer using Phi1/2 Out. SYNC is now floating and individual resistors for the 3.3K pullups. Think I may try an smd ...

Thanks Garth,

Im still working through it, but here is what I have so far. Still not sure on the address space, I need to get better at it, but where I got to was, A13 & A15 are always one within that range (A000-BFFF) and A14 is always 0

So ive fed A14 into CS1B and AND'ed A13 & A15 together ...

This reminds me of another very useful skill: being able to read a datasheet. They are usually well-organised and straightforward: the whole idea is to allow a design engineer to choose to use a part with confidence.

So, if datasheets exist, you shouldn't need to ask a slew of questions, if the ...

Ok, so if Im to look at the R65C51, does anyone have any reference implementations? I was looking at your site Garth, but it looked like the drawings were for a midi implementation?

I mean I guess im just using CS0, CS1B, RS0 & RS1 for the address decode.

PHI2 is the system clock?

ResB to the ...

Yeah I hadn't thought of that, I guess either is just as valid as the other, and it's just mixing them that's considered bad.

I am trying to move to solely CMOS, I just finished (picture) this and it's all 74LS chips, damn thing draws 1.3A at full speed. (though it also has lots of led's).

IMG ...

What would you consider low speed for the 74HC138?
That's relative, and depends on the CPU etc. A little digging in data sheets and some maths is required.

The modern W65C22 needs the chip selects stable 10ns before the clock rises, so chip selection has to be completed in 10ns less than the low ...

Why are you using that 68B50? That UART doesn't have a baud rate generator and is not CMOS-compatible. See if you can track down a non-WDC 65C51.


Ah ok, so I get the CMOS part, looks like Grants design just calls out the 6502 as opposed to 65c02, so guessing he's potentially on the older NMOS ...

Awesome Thank you, I had a suspicion it wasn't right, still struggling to calculate them, I made the mistake of only looking at the binary for $8000 which is where the A15 came from, but can see now where I went wrong.

What would you consider low speed for the 74HC138? I guess it is simpler to do ...

Ok, so ive been working through my re-design of the PCB's and trying to apply what ive learnt from you guys and Garths primer.

Ive taken a lot from Grant Searles 6502 design, and added a 65c22 (same address spaces as $6000 - $6FFF was free on Grants design, so I could wires it up the same way it ...

Just a quick update,

I put together a quick reset circuit from a 555, it's way overkill in that it gives a 2s delay. But it works consistently, regardless of whether power is initiated from the PSU, switch or pwering on it RST held and then released :)

Now just waiting om ordering a new PCB ...

Just to note, fans of Basic, BBC Basic, or Acorn's BBC Micro might enjoy Beebasm , an assembler embedded in something rather like BBC Basic. Or at bbcmic.ro (Owlet IDE) you can play with small examples. If you want to learn from scratch or explore small code snippets, easy6502 is very handy.

That ...

I did find your LCD code, but got a bit confused. Initially by the sections for Forth (I've never really touched Forth, a bit of FORTRAN, Pascal, Delphi and the usual more modern stuff, I'm really not a good coder though), and on the ASM the bit that threw me is the reference to the JSR for WAIT ...

One of my other hobbies is large-scale model railroading. I have scratched built a 1.6" scale model of an EMD F7 locomotive, in which I fabricated most of the parts from "raw" materials. As costs can quickly get out of hand if material is wasted, I heeded the ancient dictum of "measure twice and ...

There are at least two other electronics distributors in the UK that sell WDC products: BD Electronics and Coltek . Since both are British companies, you might do better price-wise with them than with Digi-Key and Mouser.


If you click through from Coltek to the shop you get to the ebay listing ...

Hi Garth,

Im currently working my way through your primer, im finding it really useful, and making notes on the bits I still don't understand properly so I can revisit those areas.

I did find your lcd code, but got a bit confused. Initially by the sections for Forth (ive never really touched ...