The Zx Spectrum Ula- How To Design A Microcomputer -zx Design Retro Computer- [repack] Jun 2026

The ZX Spectrum ULA, also known as the Ferranti F3850, was a 32-pin dual in-line package (DIP) IC that contained approximately 22,000 logic gates. Its primary function was to act as a system controller, integrating various components such as the CPU, memory, and I/O interfaces. The ULA was responsible for managing:

Enter Ferranti, a British semiconductor company. They offered the . In essence, a ULA was a pre-fabricated silicon wafer containing arrays of unconnected logic gates (AND, OR, NOT). The designer would specify a custom metal mask to connect these gates. This was cheaper than a full custom ASIC (Application-Specific Integrated Circuit) because the base silicon was generic. The ZX Spectrum ULA, also known as the

When you design a microcomputer with shared memory, you have three options: Dual-port RAM (expensive), DMA (complex), or Contention (cheap). Sinclair chose cheap. The ULA’s contention logic is why a Spectrum runs slower when drawing complex graphics. They offered the

Instead of discrete logic + Z80, use:

The Z80 CPU runs at 3.5MHz. The ULA needs to access the DRAM at 7MHz (twice as fast). Why? Because for every pixel drawn, the ULA must fetch both the pixel bitmap and the colour attribute. This was cheaper than a full custom ASIC