I have been designing an 8bit CPU from scratch, and I am about finished. I am posting the schematics here, and if anyone has any thoughts, comments or critics I'd like to know.

It has 5 general registers, 4 are 8bits and 1 is 16 bits and used for addressing. It has a full stack pointer and frame pointer. Total addressable memory is 64KB. It supports DMA (mainly for a front panel) and it has support for one maskable interrupt, which can be branched into more interrupts if needed. The CPU is microcoded. I am also thinking of adding two index registers for string operations like on an x86 CPU.

Don't mind the clock and reset circuits as they are not completed here. This schematic is for the CPU only.

Thanks!

 

You can't see it. Everything is washed out!

 

Yes, it is a bit difficult to read. You might upload it as an attachment, or split it up into blocks...

 

Hi my beloved friends,

I have zipped the schematics and attached. Please have a look and comment. Thank you!

 

wow, no comments?

 

Some of us, if not most of us, are trying to get from A to B.

We can do so by employing a $1 chip such as Atmel AVR, Microchip PIC, or TI MSP430. We can get by with an Arduino platform or we go for more computational power using an ARM chip or Raspberry Pi.

I can't see that much interest in reinventing the wheel using decades old ICs.

Don't be put off from your project or discouraged by the lack of interest.
You are in a league of its own with a very short list of followers.

 

I haven't been interested in that aspect of CPU design since the 70's when I was a tech working on refrigerator sized computers made with TTL. I troubleshot to the component level on an assembly line and the schematic was on dozens of E sized sheets. I got good at it, did it for a year, and moved on.

I worked on microprocessor projects for most of my career, but I was more interested in the physical design aspects (design rules, rule checkers, connectivity verification, yield, layout synthesis, etc).

 

I haven't been interested in that aspect of CPU design since the 70's when I was a tech working on refrigerator sized computers made with TTL. I troubleshot to the component level on an assembly line and the schematic was on dozens of E sized sheets. I got good at it, did it for a year, and moved on.

I worked on microprocessor projects for most of my career, but I was more interested in the physical design aspects (design rules, rule checkers, connectivity verification, yield, layout synthesis, etc).

Oh yes! I repaired DEC PDP-8 and PDP-15 as part of my job in the '70s.
The circuit diagrams consisted of pages and pages of 11" x 17" sheets.
I wish I had kept those.

 

Hello,

There is a lot of documentation on the PDP8 and PDP15 on the internet archive:
https://archive.org/search.php?query=pdp8&and[]=mediatype:"texts"
https://archive.org/search.php?query=pdp15&and[]=mediatype:"texts"

Bertus

 

Archived on the internet somewhere is the paper-tape code that boots an OS that I wrote for a PDP-15 hard drive back in the '70-'80s.

 

I have been designing an 8bit CPU from scratch, and I am about finished. I am posting the schematics here, and if anyone has any thoughts, comments or critics I'd like to know.

It has 5 general registers, 4 are 8bits and 1 is 16 bits and used for addressing. It has a full stack pointer and frame pointer. Total addressable memory is 64KB. It supports DMA (mainly for a front panel) and it has support for one maskable interrupt, which can be branched into more interrupts if needed. The CPU is microcoded. I am also thinking of adding two index registers for string operations like on an x86 CPU.

Don't mind the clock and reset circuits as they are not completed here. This schematic is for the CPU only.

Thanks!

Have you watched Ben Eater's excellent video set on youtube where he did basically the same thing? It's not identical to yours, but he explains not only what he did, but why. It might help...

Joel "Doc" Hopper

 

Oh yes! I repaired DEC PDP-8 and PDP-15 as part of my job in the '70s.

First all-digital design I did on my own was a PDP-8 I/O interface for experiment control and data collection. Fun machine.

ak

 

wow, no comments?

What kind of comments are you looking for? Keep in mind all you did was post some files with a short description of what they are. You give no hint as to what the purpose is or what kind of discussion/comments you are looking for, so people have no idea from what perspective they should view what you've provided, so most are going to walk on by because they have no idea what might be a helpful comment versus totally off base.