Success !

A project log for 1 Square Inch TTL CPU

A microprocessor built with TTL chips. In one square inch.

roelhroelh 10/11/2018 at 20:242 Comments

The smallest homebrew CPU in the world is working now !

Last week, I spend a few evenings changing the layout, to correct the pinout of the flash chip. Not a really easy task, this is a very crowded (only 2 sided) layout. One week ago, on thursday evening, the new layout was sent to China, and I got the pcb's yesterday. It was assembled today (I had ordered a double set of components the first time, perhaps already having the feeling that the first time would not be right). 

It is now running a simple program, it fills 6 memory locations with the 7-segment values for the digits 1 to 6, and then writes each of them to the multiplexed display in a loop. 

To show that there's nothing hidden, I disconnected the RPi, and I also show the back side of the pcb.

The display is a bit dim, that's because in the time allotted for each digit, it is only on during 3 instructions and off during 4 instructions. But in reality it is looking better. Perhaps I'll also have to make the resistors a bit lower in value. You can see the program on the  Browser-based JS assembler page. 

Back side of the pcb:

I did not work more on the application program yet. After the strike of Murphy, I decided I needed subroutines for the clock program, so I extended the microcode, also making it a bit more dense. The new microcode is now on the Javascript assembler page, but it refused to work on the NAC pcb so it has an error. Therefore, the version that you see on the picture is running with the old microcode.

I will soon update the schematics and gerbers, and describe the application pcb, the NAC, and the modifications.


Marcel van Kervinck wrote 10/11/2018 at 20:36 point

That's really cool, congratulations

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roelh wrote 10/11/2018 at 20:37 point

Thanks Marcel !

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