The Zx Spectrum Ula Official

It took a 14 MHz master clock signal and divided it down to 3.5 MHz to drive the Z80 CPU. Evolution Across Models

Detailed explanations of the famous "Snow Effect" and other design quirks. the zx spectrum ula

It handled keyboard scanning, reading audio from the EAR port, and sending sound to the internal beeper. It took a 14 MHz master clock signal