Appendix D - Z88 Clocks

Summary of the Z88 hardware clocks :

9.8327 MHz : Blink Master Clock (MCK)

   |
   |   /3
   |
  V 

3.2776 MHz : Z80 Clock (PM1)

   |
   |   /128
   |
  V 

25.6 KHz : Blink Standby Clock (SCK)

 The ratios between the Z80 clock and ticks are powers of 2 and thus directly driven by a 15 bits counter where :

• bit 0 is PM1, the Z80 clock
• bit 7 is SCK, the standby clock
• bit 10 is the beeper
• bit 14 is the 5 millisecond tick (i.e. bit 0 of TIM0)

The tick counter (TIM0 register) has a special behavior. TIM1 (second counter) is incremented when TIM0 reaches 128 (bit 7) and continues counting up to 199.

The second counter (TIM1) counts from 0 to 59 (6 bits).

Minutes registers are in fact only one large counter of 21 bits : TIM2 (8 bits) + TIM3 (8 bits) + TIM4 (5 bits).