Z86E3016PSG Datasheet, PDF (135/348 Pages) Zilog, Inc. – Z86E3016PSG

Z8 CPU
User Manual
117
treat the counter/timers as general-purpose registers, and eliminates the
requirement for special instructions.
Prescalers and Counter/Timers
The prescalers, PRE0 (F5h) and PRE1 (F3h), each consist of an 8-bit reg-
ister and a 6-bit down-counter as shown in Figure 68. The prescaler regis-
ters are write-only registers. Reading the prescalers returns the value FFh.
Figures 70 and 71 show the prescaler registers.
The six most significant bits (D2–D7) of PRE0 or PRE1 hold the prescal-
ers count modulo, a value from 1 to 64 decimal. The prescaler registers
also contain control bits that specify T0 and T1 counting modes. These
bits also indicate whether the clock source for T₁ is internal or external.
These control bits will be discussed in detail throughout this chapter.
The counter/timer registers, T0 (F4h) and T1 (F2h), each consist of an 8-
bit down-counter, a write-only register that holds the initial count value,
and a read-only register that holds the current count value (Figure 68).
The initial value can range from 1 to 256 decimal (01h,02h,..,00h).
Figure 72 illustrates the counter/timer registers.
UM001602-0904
Counters and Timers