Sir Clive’s bet was that the ULA would be cheaper than programming a CPU to do video. Today, the opposite is true: CPUs are cheap, and custom silicon is expensive. But in 1982, the ULA was the only way to build a £125 color computer.
The ULA is responsible for reading data from the video memory (the screen file in RAM) and sending it to the television screen via the video modulator. It handles the timing for both the screen data and the border color.
: Documentation of how the ULA generates video signals, including deviations from standard PAL sync signals. Sir Clive’s bet was that the ULA would
If you want to apply the architectural lessons of the ZX Spectrum ULA to design your own retro microcomputer today, you do not need to order custom silicon from a long-defunct foundry. You can replicate this entire ecosystem using modern tools.
The ULA fetches two bytes from the lower RAM: one pixel byte (8 pixels) and one attribute byte. It loads the pixel byte into a shift register, spitting out one bit at a time to determine whether the TV beam should paint "Ink" or "Paper." The attribute byte decodes the exact voltages required to form the red, green, and blue (RGB) components of that color, sending the analog signals out to the video encoder chip. 4. How to Design a Modern Retro Microcomputer Clone The ULA is responsible for reading data from
: A standard, low-cost central processing unit (CPU).
Ferranti applied a final custom metal routing layer to hardwire those connections, creating a bespoke chip for a fraction of the cost of a full-custom design. If you want to apply the architectural lessons
It handled keyboard scanning and audio input/output via the cassette interface. Key Technical Insights from the Book