A resistor DAC is not really quick-and-dirty IMO, it is pretty much a case of a simple solution that is also the right solution. I suppose you might consider the binary-ladder DAC quick and dirty, and the R-2R DAC the sophisticated solution.

For VGA (analog video), because the digital voltages are ...

Usually you validate the RWB output with the clock (by ANDing them together) since data is only valid while the clock is high but RWB can be valid way before that.
I doubt it's a fixed time of 300ns as well since that wouldn't make sense when running at +16MHz. So it depends on your clock speed ...

What do you mean by “it is not working out”? Who is the manufacturer of the 65C02? Are you sure it actually is a 65C02?

wd65c02

That is all I know currently. However, since posting I may have figured out the problem. The 6502 has a very long (~300ns) delay from the time the R/!W goes low (for a ...

Are there any glue logic families that were designed to be used with the NMOS CPUs of the late 70s and early 80s, like the 6502? Most of the retro computers seem to be built with TTL 74LS logic, even when the CPUs migrated to CMOS later in early/mid 80s (65C02, etc.).

Tangentially I'm trying to ...

Oh yeah, being able to use blind and buried vias, as well as via-in-pad and laser-drilled vias would be fantastic! However, the cost of those features are prohibitive for a hobbyist. Heck, just going from 2-layers to 4-layers is a cost increase of about 40%. I do think those features will trickle ...

Have you thought about putting parts on both sides?


I have, and I am doing that for this latest board. But I still need 4-layers. When using BGAs, it is really hard to not have parts on both sides, if only for all the bypass caps required for the BGA. It is also hard to go with just 2 layers ...

@BigEd: The 5/5 trace/space is small, but it was not even an option a few years ago when I did the first version of my board. Back then 8/8 was the smallest you could get in hobby quantity, and 4-layers were out of reach. Personally I think cell phones are almost solely responsible for the ...

Two days ago I needed to order a few boards for testing, and based on this thread I decided I would see what PCBWAY would quote. My boards are small, 52mm x 19mm (about 2" x 0.7") so I figured the cost would be low. As soon as I selected the 4-layer option (I have 4-layer boards), the price jumped ...

The FPGA is the Spartan-3E, and it does have the slew setting. I tried both fast and slow, did not help. The FPGA is on my F18A board, the trace is 8mil width and less than half an inch long. The particular system where it has problems with the Z80 is the European ColecoVision, and the VDP interrupt ...

Correct, an output going from the FPGA directly to the Z80's NMI input, with no other connections, was not working. A 100ohm resistor in-line got it working. I went down a rabbit-hole on that one, and it was no fun. Very frustrating actually, especially since it seems to be cropping up again on ...

Interesting, I never even bothered to pay attention to OSHPark's costs since my boards were never very big (never more than $15 to $20 for 3 boards). A 30 sq. in. board would certainly make me think twice though. I'll have to look into JLCPCB. I wonder how their quality compares to OSHPark?

Bill, what happens if you tri-state one side of that circuit? What does the output on the other side do?

That is true, 3.3V logic can normally drive the input of the 5V 74LSxxx logic that is typical in the retro computers we are usually dealing with. I have had situations where it has worked, worked but needed an in-line resistor (100ohms), and totally failed.

On the flip side, driving a 3.3V input ...

It seems certain the 3E can provide appropriate I/O for your project -- which sounds pretty cool, btw :) -- but you'll need to know what you want and how to ask for it. Thanks! I've noodled around with FPGAs for a while - this is my 3rd board from Digilent, and I've had it a few years but haven't ...

If you are interfacing with legacy 5V TTL and such, I recommend the dual-voltage devices like SN74LVC8T245DGVR and others in that family. I have also used the 245 variant that is a 3.3V device with 5V tolerant I/O, and they can't take any abuse from the 5V side in case of things like glitches and ...