Hello everyone! Hope you're all doing OK! It's been a while. I'm afraid I turned to the dark-side over summer, getting into audio, designing and building power amplifiers (two built - a class-D 10W stereo amp, and a class-AB 30W dual-mono amp, along with their power supplies). It took me away from ...

This is version 1 of the Flash ROM daughterboard that I somewhat prematurely had fabbed, before I'd really given any thought to interfacing a 3.3v chip with a 5v system.
IMG_5549.JPG
As you can see it is missing any kind of logic level shifting, and so is mostly useless (the little chip in the ...

Hi Garth, very interesting and useful, thanks very much for the info. Yes, this was a bit of a stab in the dark TBH. I failed to mention that the 1K resistor values were the default values provided by the schematic software and that I'd not yet given any proper thought to what those values should be ...

I've made some changes to the Control Unit, most notably around the clock generation, and some changes to net labels to make them more consistent. I've included my attempt at a single-instruction step solution, which makes use of a 74HC112 JK FlipFlop because of its falling edge clock. I'm not sure ...

Here's how the microinstructions are currently organised across the two 16-bit ROMs. It's worth mentioning that a hint Dieter's gave me about the Z and N flags are always affected together saved me a slot, which was eventually filled with S.DN (Stack count direction). That in itself saved quite a ...

Hi all,

Thanks for the responses and info regarding connectors. All very helpful.

Having run them past him and made some changes following his advice, Dieter has recommended I post the schematics here for wider comment. So here goes!

First the Control Unit. This is the circuit that's changed the ...

Thanks for the responses, all.

Am I correct in assuming there's nothing electrically advantageous to using ribbon cable over edge connectors/sockets? Is it more an ease of use kind of thing? Dr Jefyll, you suggested that it might be cheaper to run ribbon cable. I can get 10xPCIe16 sockets for £22 ...

My gut feeling is that modular is better - the question is whether you can slice the thing at its joints.
Thanks. I've got things modularised currently, so no real issue with what goes on which board, the problem I'm trying to solve is how to transmit the bus, clock and control signals efficiently ...

Folks - a quick opinion poll if I may.

I'm concerned that my current design, which features a backplane with 10-or-so cards stacked up using PCIe x16 interconnects (yes, that's different from what I posted earlier - long story short, 120 pins on the smaller sockets wasn't going to cut it) is going ...

Hi all. Hope you're all doing OK.

It's been quite a while since my last update but I wanted to start getting some of the schematics and PCBs on here for thoughts and comments. Things are progressing quite nicely with the project - I have schematics for the Register, Status Register, ALU, Buffers ...

Of course - that makes sense now.

Thanks.

Sorry if this has already been asked elsewhere in this topic, but why are the two ICs 74'132 and 74'245 thru-hole DIP parts when all the other logic ICs are SMD?

Hello everyone. It's been a while. Firstly a very belated thanks Drass for your response - it was very helpful in allowing me to better understand the "B" bit and how it works.

So, bigish news - I've been working hard on the My6502 emulator since I felt I'd neglected it somewhat recently. I've now ...

IIRC the C74-6502 TTL CPU runs the BRK microcode when it comes to RES, NMI, IRQ by forcing the instruction register to $00,
and the vector address for the address bus is generated by hardware.
Of course. It's obvious now!

I misunderstood when... ...one of the first things your reset routine ...

A brief update.

I've modified all the "MicroCodeAssembler" and the "ControlUnit" code in the emulator to move the fetch-next-instruction to be the last thing in each instruction, as advised. I realised this would be advantageous for a couple of reasons, but one unexpected bonus was that I've clawed ...