TTL CPU schematic done

A project log for One-instruction TTL Computer

A breadboard-able computer which uses only a single instruction - MOVE

Justin DavisJustin Davis 09/29/2017 at 14:530 Comments

I've completed the schematic for the CPU portion of the design.  It's a pretty big design - I'll post it here shortly.  There's 21 chips just for the CPU.  And just placing them on a PCB, it's about half the size of a standard piece of paper, but routing might make this bigger.  I have a 16-bit address bus and an 8-bit data bus to route everywhere, so I will almost certainly have to do a 4-layer board.  Estimating the cost of this - from EasyEDA this size of a 4-layer board is about $46+$8 shipping for 5.  

Ok, I just checked if I double the size of the board (for the peripherals, clock, power) the price goes to $59+$8.  So I may just put everything on a single board.  It would cost a lot more to make two boards of the same size of a single large board.  I'll still have an expansion bus for debugging and possible future projects (video out maybe?)  I'll just have to make sure I get it right the first time.  But then, it's only $59+$8 to rev it, right?