SH79F166APSLASH044PR datasheet(93/113 Pages) SINOWEALTH

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SH79F166A

8.9 Watchdog Timer (WDT) and Reset State

8.9.1 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 Reset

To enhance the anti-noise ability, SH79F166A 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.

Watchdog Timer

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:

SH79F166AP/044PR Datasheet(PDF) 93 Page - SINOWEALTH Electronic Ltd