I'm a beginner interested in CPLDs as well and was wondering who's tools have the best Linux support. Any un*x users care to comment?

Driving the UK101 odd the Speccy's power supply and clock signal is a possibility but will require some thought as I don't want to solder wires direct to the edge connector.
Well, this suggestion is definitely a hack and wouldn't be recommended for long term use, but do you have any clothespins ...

OE\ or W\ need to be low when Φ2 is high , not low.
Somehow I managed to get the phase of Φ2 backwards. Thanks for pointing that out. I'll have to go through the rest of the circuit and see if I've made the same mistake elsewhere.

Yes, I forgot some call Φ0 "Φ2 in". On the DIP, it's pin 37.
Yep ...

I don't want to be controversial, but I'm not sure this is true. Garth has a specific point about 6522, and BDD has a general rule which he acknowledges isn't used by everyone.
So, out of curiosity, do you qualify device selection based on PHI2?

My feeling is that I've seen conversations but I ...

The SRAM's OE\, CS\, and WE\ inputs are just that, meaning active low, not active high. ... You'll need to change some logic.
Thanks for pointing that out. The SRAM's /E pin (/CE) should be tied to ground, not Vcc, and likewise with the FRAM's /G (/OE) pin. I somehow got them mixed up when I was ...

Not sure what the thing will do if it's in ROM and the RAM is empty (or vice versa). Will it cycle?
Well, the first thing it will do is go to the reset vector 0xEAEA. Then, if that's in the ROM area, it'll start executing NOPs until it reaches 0xFFFF. At that point, the program counter wraps ...

I've made some more changes to my design . I added a power connector, some pull-up resistors, clock generation, and a reset controller. I also fixed and improved the address decoding, rearranged the bus headers, and redid the whole layout using bus lines, which makes it a lot less messy.

The power ...

I think I've figured (at least part of) my question about (potentially) unused inputs on my bus. Basically, I need pull-up or pull-down resistors to set the default state of these inputs. However, I don't know exactly what size of resistors to use.

I came across an informative article Implications ...

I haven't been working on my mainboard design much. (I got distracted with ideas for a USB FRAM/EPROM programmer.) However, I came up with a new address decoding scheme (using a '138), which lead to a more organized (if still unpopulated) memory map.

As before, the low 32k is the SRAM. The high 32k ...

Sorry about the 404, I'm such a scatter brain sometimes. It's fixed now.

Unused inputs should be tied to a defined logic level. You could for example define a "logic 1" signal with a single 10kOhm to VCC and use that for all inputs. OTOH I normally connect them directly to VCC, but that has bitten ...

I'm assuming he means that building a 13 input NAND using discreet components with less inputs would add gate delays.

I've always wanted to build a computer. So lately I've been working on a design for a simple 6502 based machine. As I don't have a whole lot of electronics experience, I'm trying to keep things simple for now.

I've started working on a design, which you can download here . The generic logic gates ...

Only quick: you could use a LUT and use one bit in the LUT to define if the LUT entry is valid, and if not fall back to your read-from-main-memory approach (using the LUT as cache). That is, as far as I understand, what current CPUs do.
Well, they actually use content addressable memory for the ...

One of my earlier designs actually used a dedicated RAM to store the page table, however, I decided against it because of the need to reload the entire table every task switch. If one used larger page sizes, the overhead of doing so wouldn't be too bad, but 256 byte pages just feel natural on the ...

Oh, I'm aware of the 65816, but it kinda goes against the grain of this idea. Basically, the idea was to build a full-featured MMU for a processor that was never designed to have one. It's kinda a silly bit of overkill, but it's interesting from a design perspective. To be honest, the idea (to make ...