SH79F024XU datasheet(74/92 Pages) SINOWEALTH

74 / 92 page

SH79F

SH79F082

082

8.7

7 Watchdog

Watchdog

Watchdog Timer

Timer

Timer (WDT)

(WDT)

(WDT) and

and

and R

Reset

eset

eset S

State

tate

8.7

7.1

.1 Feature

Feature

�

Auto detect Program Counter (PC) over range, and generate OVL Reset

�

WDT runs even in the Power-Down mode

�

Selectable different WDT overflow frequency

OVL

OVL Reset

Reset

To enhance the anti-noise ability, SH79F082 built in Program Counter(PC)over range detect circuit, if program counter value

is larger than flash romsize, or detect operation code equal to A5H which is not exist in 8051 instruction set, a OVL reset will

be generate to reset CPU, and set WDOF bit. So, to make use of this feature, you should fill unused flash rom with A5H.

The watchdog timer is a down counter, and its clock source is an independent built-in RC oscillator, so it always runs even in

the Power-Down mode. The watchdog timer will generate a device reset when it overflows. It can be enabled or disabled

permanently by the code option.

The watchdog timer control bits (WDT.2-0) are used to select different overflow frequency. The watchdog timer overflow flag

(WDOF) will be automatically set to “1” by hardware when overflow happens. To prevent overflow happen, by reading or

writing the WDT register RSTSTAT, the watchdog timer should re-count before the overflow happens.

There are also some reset flags in this register as below:

SH79F024XU Datasheet(PDF) 74 Page - SINOWEALTH Electronic Ltd