SH79F6489PSLASH080PR datasheet(125/152 Pages) SINOWEALTH

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SH79F6488/SH79F6489

125

8.11 Watchdog Timer (WDT) and Reset State

8.11.1 Features

 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, SH79F6488/SH79F6489 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.

Note: After base timer or LCD on, if WDT is on ,WDT cannot be turn off in Power-Down mode. Therefore, users need to read or

write RSTSTAT register in case to WDT overflow.

SH79F6489P/080PR bảng dữ liệu(PDF) 125 Page - SINOWEALTH Electronic Ltd