The System core contains the essential modules required for the normal operation of the Whiz80. Missing modules may prevent the Whizz80 computer from functioning correctly. This core connects to the submodules by a system bus.
The System bus consists of 40 bus lines. 16-bit Address line (A0-A15), 8-bit Data line (D0-D7), Power (+5v, GND) and 9 control lines (/CLOCK, /RESET, /MEMREQ, /IORQ, /RD, /WR, /INT, /M1/ /WAIT) and 5 optional spare lines (SPARE1, SPARE2, SPARE3, SPARE4, SPARE5).
Each module connects to the system bus. The following 6 modules make up the system core (5 standard, and 1 special)
The power module supplies regulated power to the whole whizz80 system. Output of this module is via the system bus, and currently consists of +5v, ground and any reset signals.
The clock module outputs a clock signal to the system bus that controls the timing of everything. A simple version of this module might just be an oscillator or a 555 timer, or it could be as complicated as a stepper single shot timer. As long as the output can generate a clean square wave. You could make many different types of clock modules, and simply swap them out to select your desired clock speed.