AT89C51CC02CA-RATUM datasheet(69/159 Pages) ATMEL

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AT/T89C51CC02

4126L–CAN–01/08

Watchdog Timer

T89C51CC02 contains a powerful programmable hardware Watchdog Timer (WDT) that

automatically resets the chip if it software fails to reset the WDT before the selected time

interval has elapsed. It permits large Timeout ranging from 16ms to 2s @f

OSC = 12 MHz

in X1 mode.

This WDT consists of a 14-bit counter plus a 7-bit programmable counter, a Watchdog

Timer reset register (WDTRST) and a Watchdog Timer programming (WDTPRG) regis-

ter. When exiting reset, the WDT is -by default- disable.

To enable the WDT, the user has to write the sequence 1EH and E1H into WDTRST

enabled, it will increment every machine cycle while the oscillator is running and there is

no way to disable the WDT except through reset (either hardware reset or WDT over-

flow reset). When WDT overflows, it will generate an output RESET pulse at the RST

pin. The RESET pulse duration is 96xT

OSC, where TOSC=1/fOSC. To make the best use of

the WDT, it should be serviced in those sections of code that will periodically be exe-

cuted within the time required to prevent a WDT reset

Note:

When the watchdog is enable it is impossible to change its period.

Figure 31. Watchdog Timer

WDTPRG

RESET

Decoder

Control

WDTRST

Enable

14-bit Counter

7-bit Counter

Outputs

Fwd Clock

RESET

AT89C51CC02CA-RATUM Datasheet(PDF) 69 Page - ATMEL Corporation