If you've ever used a device with a WAIT line, you know that the system operates at full speed unless something causes it to slow down. One of those things is a WAIT line. Now, if you're not using the timers or serial port, unlikely in your world, you can fiddle with the clock.

There are some 805x types that have SFR control of what the hardware does with the oscillator in the course of producing the system clock. Some can increase or decrease the amount by which the oscillator is divided. Some can even multiply the clock by a programmable constant. I've yet to see an 805x type that has a WAIT line, though.

If you use a WAIT line, it slows down the CPU only when it has to, which means it runs faster than it would run if it had to synchronize with a slower peripheral all the time it was doing something else. That's what makes, say, a 20 MHz Z80 work with an i8255.

RE