Z86L0808PSC datasheet(16/26 Pages) ZILOG

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Z86L04/L08

Z8 8-Bit Cost-Effective Microcontrollers

Zilog

P R E L I M I N A R Y

DS97LVO0901

FUNCTIONAL DESCRIPTION (Continued)

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 are two 8-bit programmable

counter/timers (T0 and T1), each driven by its 6-bit pro-

grammable prescaler. The T1 prescaler is driven by inter-

nal or external clock sources. (Figure 14).

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

source by any integer number from 1 to 64. Each 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 or IRQ4 (T0) 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 counters, but not the prescaler, are read at any time

without disturbing their value or count mode. The clock

source for T1 is user-definable and is either the internal mi-

croprocessor clock divided by four, or an external signal in-

put through Port 3. The Timer Mode register configures the

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

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

gate input for the internal clock.

Figure 13. 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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