The ULA generates the master clock signal (typically 14 MHz) and divides it down to create the CPU clock (3.5 MHz). The book explains the specific timing tolerances and why the Spectrum's CPU speed was slightly variable between different motherboard revisions.
Don't design a new ULA. Instead, use a modern CPLD (Complex Programmable Logic Device) like the XC9572XL or an FPGA (Sipeed Tang Nano). The PDF will teach you the of the original ULA. Replicate them in Verilog or VHDL. The Zx Spectrum Ula How To Design A Microcomputer Pdf 57l
💡 : This book is essential for those building hardware clones (like the Harlequin) or learning retro-computer design. The ULA generates the master clock signal (typically