The Zx Spectrum Ula- How To Design A Microcomputer -zx Design Retro Computer- -

If you are restoring a , put a finger on the ULA. If it is cold and the screen is white, the ULA is dead. If it is hot and the screen is flickering vertical lines, the lower RAM (attached to the ULA) is dead.

On your own computer, decide if you want shared video RAM. For a simpler design, use dual-port RAM or separate video RAM. For authenticity, implement contention logic in your ULA. If you are restoring a , put a finger on the ULA

: Details how the ULA handles the shared 16KB bank of RAM where both the CPU and the display circuitry compete for access. On your own computer, decide if you want shared video RAM

Steve Vickers, the mathematician tasked with writing the ROM (Read-Only Memory) software, walked into the lab one afternoon. "The machine keeps crashing when I try to draw a circle in high-res mode," Vickers said, holding a circuit board. : Details how the ULA handles the shared

To save memory, he designed the ULA to handle color in 8x8 pixel blocks (attributes) rather than for every single pixel. This created the Spectrum's famous "color clash," but it was the only way to make the machine affordable.

"If a function can be done in software, do it in software. If it saves a chip to do it in hardware, do it in the ULA."