3. How to Design a Modern Microcomputer: Replicating the ULA
An EPROM can be used as a look-up table to generate the complex timing signals required for video output. Design Challenge:
Program your CPLD to act as the traffic cop. It must intercept CPU requests, generate horizontal and vertical sync signals for your screen, and decode memory addresses. 2. Choosing the Brain (CPU vs. Emulation) It must intercept CPU requests, generate horizontal and
You must manually manage the timing windows where the CPU can write to video memory without causing "snow" or screen corruption. 3. Emulation on Microcontrollers For portable, handheld designs, the Raspberry Pi Pico is a popular choice. Raspberry Pi PicoZX Project: Projects like the
If the CPU tries to read or write to this memory while the ULA is drawing the visible part of the screen, the ULA physically forces the CPU to wait by pulling the Z80's WAIT pin low. This complex timing choreography is one of the hardest parts of a ZX design to replicate accurately. The I/O Hub: Keyboard, Tape, and Speaker Emulation) You must manually manage the timing windows
It handled pixel and attribute (color) data from memory to generate a PAL video signal.
A 256x192 monochrome bitmap dictates where pixels are drawn. routing signals between a physical Z80
Color is applied in 8x8 pixel blocks. This "limitation" defines the retro aesthetic. 🔋 Making it Portable
To design a modern retro computer or clone, your core logic architecture must replicate the four primary responsibilities of the original ULA: 1. Video Generation and Timing
Excellent if you want to use a real hardware Z80 CPU. A CPLD has enough logic gates to act purely as the ULA, routing signals between a physical Z80, physical RAM, and the display.