The book "The ZX Spectrum ULA: How to Design a Microcomputer" provides a detailed analysis of the ULA chip's design and functionality, and is considered a valuable resource for anyone interested in the history of the ZX Spectrum and the development of microcomputers.
ZX Spectrum ULA, How to Design a Microcomputer, Digital Logic, Ferranti, Retro Computing, PDF 57L The Zx Spectrum Ula How To Design A Microcomputer Pdf 57l
One of the most ingenious parts of the ULA design was the "contention." The ZX Spectrum runs at 3.5 MHz. The ULA needs to read video memory at 1.75 MHz. When the CPU tries to access address $4000-$7FFF (display file), the ULA physically pulls the !WAIT line low. The book "The ZX Spectrum ULA: How to