My FPGA is generating the phi2 to the 65c02, so it is synchronized. However, I know I still need to sync the signals coming from the 65c02 into the FPGA. The original system schematic relied on the pho2 from the original NMOS 6502B to set various signals. But since I’m using the WDC version, I am ...

Thanks a ton for the feedback. At least I have a better idea that I’m on the right path.

I created a very simple test project to allow me to check the incoming data bus value on r_w active low (cpu write) for a given address. I’m using the BB primitive for the Lattice ECP5 in synthesis and the ...

Hi all,

I’m working a project that is based on an existing TTL logic-based design, where a 6502 shares a data bus with a 6522 and a ROM chip. It then shares this bus with external peripherals with an old DM8304 bidirectional buffer acting as gatekeeper which is controlled by other logic.

I’m ...

Michael - Thanks. That's what I kind of thought - that delays were only applicable in simulations, not in synthesis.

Andrew J - that's a nice collection of 74 series logic. I'll compare your VHDL to my Verilog and see how far I was off.

Chris Z

Hi all,

I’ve finally dipped my toes into the FPGA pool for the purpose of converting existing schematics onto the FPGA using Verilog on a TinyFPGA-BX. I’m slowly getting the hang of Verilog and replicating 74-level gates into modules I can use for a larger glue-logic circuits to be used in my ...

The Uzebox is a retro console using an ATmega644 that does something similar, but because it runs at 28.6Mhz (8 times the NTSC color burst frequency), it can use software to generate the video signals, rather than external hardware.

This is exactly the kind of hint I’ve been looking for. I’m at a ...

Fantastic work, and thanks for sharing the beefy pics.

Relevant to me, you buried the lead with using the Mega for video. I'm at a point in my project where I'm looking into various methods to generate different video modes. Using my Arduino Mega2560 was one idea.
With yours, are you using a ...

I knew the subject of clocks and oscillator design had to have been discussed here previously. One such thread included this link: http://www.ti.com/lit/an/snoa676/snoa676.pdf
It answered a few questions with regard to pros and cons of various clock designs. A good thread was this:
http://forum.6502 ...

Thanks. My test board currently has the crystal across a couple of 1k resistors and 74LS04 with 68uf capacitor, similar to the NMOS oscillator in the 6502 Primer. Works, but how accurate will it hold? In my research, the transistor/ capacitor arrangement is said to be more accurate.

Hi,

In my retro project, I’m going to tackle clock generation, ala Apple II, with a 14.3MHz crystal. I’ll need to divide it down to various frequencies for video, disk drive, CPU clock, etc.

I’m working from existing schematics. But it’s all based on the 14-ish MHz clock frequency. To make this ...

Believe me, you're not the only one enjoying and benefiting from these discussions. I'm working on my own single-board machine and the issues/questions you've brought up are the same as I have had. These guys are phenomenal in the time and patience it takes to help a newcomer get their projects ...

The Apple /// is such an odd-duck in the 8-bit computing world, in that it included everything and the kitchen sink, but also had an amazing amount of innovative capability for the time. I was tempted to start with a simpler SBC, then graduate to an Apple II-like system. But the /// just deserves ...

Hi all,
I'm building an Apple /// clone as my "first 8-bit microcomputer" project computer. And yes, I know... "An Apple /// for your first project? Do you also enjoy punching yourself in the face?" But I'm taking it very slowly.

Regardless, I'd like to use a 28c64 EEPROM for my ROM. Since the ...