The Zx Spectrum Ula- How | To Design A Microcomputer -zx Design Retro Computer- [extra Quality]

Through this research, we know the ULA relies on a sequence of internal counters. As the video beam sweeps across the television screen, the ULA increments its horizontal and vertical counters. These counters act as a pointer, calculating the exact memory address of the pixel and attribute data needed for that microsecond of video playback.

This is the ULA’s most famous "quirk." Since the ULA and CPU both need the memory to function, the ULA would "halt" the CPU clock whenever it needed to draw the screen, leading to what programmers call contended memory . Through this research, we know the ULA relies

The ULA handles the baseline input/output. When the Z80 executes an I/O instruction to Port 0xFE , the ULA intercepts it to: Read the matrix keyboard rows. Read the cassette tape input ( port). This is the ULA’s most famous "quirk

A modern FPGA (like the Terasic DE2-115) can emulate the entire behavior of the original Ferranti ULA and Z80 CPU. Read the cassette tape input ( port)