This 6502 Made From 74-Series Logic Can Run At 20 MHz

If you always wished you could get closer to the hardware with the 6502 in your classic microcomputer you’re in luck, because [Drass] has created a beautiful implementation of a 6502 using TTL logic chips. What makes it special is that it sits on a very neat set of PCBs, and due to its use of 74AC series logic it can run at much higher speeds than the original. A 20 MHz 6502 would have been revolutionary in the mid-1970s.

Neat reworking of what looks to be a reversed bus.
Neat reworking of what looks to be a reversed bus.

Through a flying ribbon cable, it can plug directly into the 6502 socket on classic microcomputers, and the website shows it running a variety of software on a Commodore VIC20. There is also a custom SBC as part of the suite, so no need for a classic micro if you want to put the CPU through its paces. The boards are not quite perfect, the website has a picture of some very neat reworking where it appears that a bus has been applied to a chip in reverse, but it certainly has the feel of a professional design about it.

This is a very tidy 6502, but it’s not the first we’ve seen and neither is it the most dis-integrated. There is a fascinating world of 74 logic CPUs to be explored, so it’s difficult to pick only one other to show you.

Thanks [Jeff] for the tip.

1MHz, 2 Boards, 4 Bits And A Homebrew CPU

[Agp.cooper] saw a vintage 4Kx4 bit RAM chip and decided that it needed a CPU design to match. The TTL design fits on two boards and has a functional front panel.

This custom CPU project has a few interesting bits worth noting. First, it is small enough that you can wrap your head around it pretty easily. And [Agp.cooper] gives  a good account of the instructions set architecture choices he considered and why he settled on the final design.

Continue reading “1MHz, 2 Boards, 4 Bits And A Homebrew CPU”