Z86C34 datasheet(42/70 Pages) ZILOG

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Z86C34/C35/C36/C44/C45/C46

CMOS Z8® MCUs with ASCI UART

ZiLOG

P R E L I M I N A R Y

DS007601-Z8X0499

FUNCTIONAL DESCRIPTION (Continued)

WDTMR During HALT (D2).

This bit determines whether

or not the WDT is active during HALT mode. A 1 indicates

active during HALT. The default is 1.

WDTMR During STOP (D3).

This bit determines whether

or not the WDT is active during STOP mode. Because XTAL

clock is stopped during STOP mode, the on-board RC must

be selected as the clock source to the POR counter. A 1 in-

dicates active during STOP. The default is 1.

Note: If permanent WDT is selected, the WDT runs in all

modes and can not be stopped or disabled if the on board

oscillator is selected as the clock source for WDT.

Clock Source for WDT (D4).

This bit determines which

oscillator source is used to clock the internal POR and WDT

counter chain. If the bit is a 1, the internal RC oscillator is

bypassed and the POR and WDT clock source is driven from

the external pin, XTAL1. The default configuration of this

bit is 0 which selects the internal RC oscillator.

WDTMR Register Accessibility.

The WDTMR register is

accessible only during the first 60 internal system clock cy-

cles from the execution of the first instruction after Power-

On Reset, Watch-Dog Reset, or Stop-Mode Recovery. Af-

ter this point, the register cannot be modified by any means,

intentional or otherwise. The WDTMR cannot be read and

is located in bank F of the Expanded Register Group at ad-

dress location 0FH (Figure 30).

Note: The WDT can be permanently enabled (automatically

enabled after RESET) through a mask programming op-

tion. The option is selected by the customer at the time

of ROM code submission. In this mode, WDT is always

activated when the device comes out of RESET. Execu-

tion of the WDT instruction serves to refresh the WDT

time-out period. WDT operation in the HALT and STOP

Modes is controlled by WDTMR programming. If this

mask option is not selected at the time of ROM code sub-

mission, the WDT must be activated by the user through

the WDT instruction and is always disabled by any reset

to the device.

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