The ULA chip in the ZX Spectrum performed several critical functions:
This guide only scratches the surface. If you are serious about diving into ZX design, you need the right documentation:
If you are looking to design a portable or modern ZX-compatible machine today, you generally have two paths: The ULA chip in the ZX Spectrum performed
Because the original ULA was so difficult to reverse engineer, many cloners found a workaround: they replaced the single ULA with multiple smaller, off-the-shelf logic chips to replicate the same functions. This is the ultimate exercise in "glue logic." A modern example of this is the Harlequin . The Harlequin is a 100% compatible 48K Spectrum built using a CPLD (Complex Programmable Logic Device) combined with standard transistors for the analog sections (audio and video).
Think of a ULA as a "semi-custom" chip. It came from the factory with a grid of logic gates (NAND and NOR gates) already printed, but unconnected. An engineer would then design the connections between these gates to create specific functions. The Harlequin is a 100% compatible 48K Spectrum
Is your goal a or a modernized version with SD card support?
It handles a 5x8 matrix keyboard using half-row address lines ( A8 through A15 ) to read the state of the keys via data lines D0 to D4 . An engineer would then design the connections between
It reads the display data from RAM, translates it into pixel and color information, and generates the television signal.
Perhaps the most exciting frontier for ZX Spectrum design today is portability. Several DIY projects have transformed the Speccy into a handheld device that Sinclair's designers could only have dreamed of.