You really need to establish your objectives and motivation for doing this because there are many ways to approach this.

1) Replicate a retro machine exactly as it was.
2) Build a computer based on a defined CPU (e.g. MOS 6502) that must run existing programs.
3) Modify sections of the machine with LSI chips such as MC6845 video controller. There is no guarantee that existing software will run.
4) Modify the video controller for monochrome or color graphics display. Existing software will definitely not work unless you make some major software patches.

Now, if you want to play around with a minimalist computer design, STM32 ARM MCUs can drive a VGA monitor with no external ICs required.

 

RCA1802, MOS6502, MC6800, MC6809, MC68000, were all great CPUs at the time.
The world of computers has moved on by leaps and bounds since then.
Why do you want to recreate a computer based on 50-year old technology?

 

You really need to establish your objectives and motivation for doing this because there are many ways to approach this.

1) Replicate a retro machine exactly as it was.
2) Build a computer based on a defined CPU (e.g. MOS 6502) that must run existing programs.
3) Modify sections of the machine with LSI chips such as MC6845 video controller. There is no guarantee that existing software will run.
4) Modify the video controller for monochrome or color graphics display. Existing software will definitely not work unless you make some major software patches.

Now, if you want to play around with a minimalist computer design, STM32 ARM MCUs can drive a VGA monitor with no external ICs required.

My motivation is learning older period based TTL design and function. As I mentioned previously I'm looking at the Apple 1 design with modifications so that is 6502 based. Text video output is fine like the original Apple 1 no graphics. Thanks.

 

RCA1802, MOS6502, MC6800, MC6809, MC68000, were all great CPUs at the time.
The world of computers has moved on by leaps and bounds since then.
Why do you want to recreate a computer based on 50-year old technology?

Why not? That is what interests me at the current time. Thanks.

 

That sounds wonderful.
After you have wired all the circuits together, how are you going to get the code to run? I hope that you figured out how to do this before you get started.

 

That sounds wonderful.
After you have wired all the circuits together, how are you going to get the code to run? I hope that you figured out how to do this before you get started.

Thanks. The code can be loaded by typing it in or loading it from a ROM card or an audio source through an Apple cassette interface since it will functionally be an Apple 1.

 

I can see that you have not yet figured out how to do this.

When you assemble a DIY computer from scratch with 50-year old technology, it is like an empty box with nothing inside. There is no way to get any code into it. It is like building a car and you forgot to put batteries or a gas tank on it.

You cannot load code into the machine unless it already has working code. In other words, it takes code to load code. In the 1970s, we loaded code manually on the front panel via toggle switches. We had to do it so often that the short 12 lines or so of binary codes are engraved in our brains.

 

11 years ago another member started a similar thread.
Then we never heard back.

https://forum.allaboutcircuits.com/threads/build-my-own-computing-system.72694/

 

I can see that you have not yet figured out how to do this.

When you assemble a DIY computer from scratch with 50-year old technology, it is like an empty box with nothing inside. There is no way to get any code into it. It is like building a car and you forgot to put batteries or a gas tank on it.

You cannot load code into the machine unless it already has working code. In other words, it takes code to load code. In the 1970s, we loaded code manually on the front panel via toggle switches. We had to do it so often that the short 12 lines or so of binary codes are engraved in our brains.

You seem to not understand correctly what I am doing. I have built fully working Apple 1 replicas before and this will just be a modified version. I'm not changing the Apple 1 prom wozmon code. I am not reinventing the wheel only modifying it.

 

11 years ago another member started a similar thread.
Then we never heard back.

https://forum.allaboutcircuits.com/threads/build-my-own-computing-system.72694/

Okay, so I'm not sure how that applies here, but thanks for sharing. A lot of people are successful in doing what they want without reporting back to those who helped. It's part of human nature to forget or get busy with other things in life.

 

What I am hinting at is you need to be able to program some EPROMs or have access to preprogrammed Apple PROMs.

If you really would like to have some fun, I used to trouble-shoot PC mother boards. I would remove the BIOS ROM and plug in my own SRAM adapter. With this I was able to run my own diagnostic code and pinpoint the cause of failure on the mother board.

 

What I am hinting at is you need to be able to program some EPROMs or have access to preprogrammed Apple PROMs.

If you really would like to have some fun, I used to trouble-shoot PC mother boards. I would remove the BIOS ROM and plug in my own SRAM adapter. With this I was able to run my own diagnostic code and pinpoint the cause of failure on the mother board.

I have programmed eproms and other devices for over 25 years. I have a half dozen different programmers and a variety of eprom, prom, and eeprom chips so that's not difficult. I have built diagnostic cards for Apple 1 and other computers but PCs always seemed quicker and cheaper to fix by replacing parts. Diagnostics cards are only good for partial failure testing.