Z86L02 datasheet(21/37 Pages) ZILOG

21 / 37 page

Z86C02/E02/L02

Zilog

Cost Effective, 512-Byte ROM CMOS Z8® Microcontrollers

DS96DZ80301

P R E L I M I N A R Y

Stack Pointer. The Z8 has an 8-bit Stack Pointer (R255)

used for the internal stack that resides within the 60 gen-

eral-purpose registers. It is set to 00Hex after any reset.

General-Purpose Registers (GPR). These registers are

undefined after the device is powered up. The registers

keep their last value after any reset, as long as the reset

occurs in the VCC voltage-specified operating range. Note:

Counter/Timer.

There

8-bit

programmable

counter/timers (T1), each driven by its 6-bit programmable

prescaler. The T1 prescaler is driven by internal or external

clock sources. (Figure 15).

The 6-bit prescaler divide the input frequency of the clock

source by any integer number from 1 to 64. The prescaler

drives its counter, which decrements the value (1 to 256)

that has been loaded into the counter. When both counter

and prescaler reach the end of count, a timer interrupt re-

quest IRQ5 (T1) is generated.

The counter can be programmed to start, stop, restart to

continue, or restart from the initial value. The counters are

also programmed to stop upon reaching zero (Single-Pass

mode) or to automatically reload the initial value and con-

tinue counting (Modulo-N Continuous Mode).

The counter, but not the prescaler, is read at any time with-

out disturbing its value or count mode. The clock source for

T1 is user-definable and is either the internal microproces-

sor clock divided by four, or an external signal input

through Port 3. The Timer Mode register configures the ex-

ternal timer input (P31) as an external clock, a trigger input

that is retriggerable or non-retriggerable, or used as a gate

input for the internal clock.

Figure 14. Register Pointer

The upper nibble of the register file address

provided by the register pointer specifies

the active working-register group.

R253

(Register Pointer)

I/O Ports

Specified Working

The lower nibble

of the register

file address

provided by the

instruction points

to the specified

R15 to R0

R15 to R4

R3 to R0

R15 to R0

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