This article contains a brief overview and a background of the A-Z80 CPU created for FPGA boards and a ZX Spectrum implementation tied to it.
A-Z80 is a conceptual implementation of the venerable Zilog Z80 processor targeted to synthesize and run on a modern FPGA device. It differs from the existing (mostly Verilog) Z80 implementations in that it is designed from the ground-up through the schematics and low-level gates.
...continue reading "A Z80 From the Ground Up"
Data bus on the Z80 processor is 8 bits wide. Data bus wires carrying information within the chip itself do not simply connect to package pins and out to the world - the gate circuitry of each bit is quite complex. This article presents a transistor level schematic of a data bit’s gate which I reverse-engineered from a die photograph.
...continue reading "The Anatomy of a Z80 Gate"
After reading excellent Ken Shirriff's blog on reverse-engineering parts of the Z80 CPU, I decided to learn how to decipher some of the chip die-shots myself. It turns out not to be that difficult if you follow certain guidance which I will describe in this post.
...continue reading "Z80 Instruction Register deciphered"
Here I show a trace of every single Z80 instruction as run by that setup. I also outlined some of the tests created manually that clarified few situations which were not too obvious (to me) after reading various pieces of documentation.