A microprocessor computer system designed from 7400 series NAND gate chips with tri-state buses.
The first, and most important, limitation of this project is cost. This project stemmed from a desire to build a simple processor from first principles. I had originally wished to order the end result of the layout through a multi-project wafer service but the cheapest prices I had found were 300 Euros/mm^2 for .7um feature size, so I determined the price of a full processor to be significantly out of my budget. Even the next best thing, building the logic from complementary pair transistors on PCB proved to be prohibitively expensive, so I settled for designing the logic of the system out of 7400 series NAND gates with tri-state buffers. Because the NAND chips are relatively inexpensive, the most costly portion of this design was the large PCB, with a price of $160 for 12"x10".
So with the design decision made to develop this system out of NAND gate chips, I set forth designing the logic. The logic-based requirements for the computer are: performs as a general purpose computer, has an 8-bit register size