ADE75 datasheet(92/148 Pages) AD

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ADE75xx/ADE71xx

Preliminary Technical Data

Rev. PrE | Page 92 of 148

necessary so that the WDCON SFR is protected from code execution upsets that

might unintentionally modify this SFR. Interrupts should be disabled during this

operation due to the consecutive instruction cycles.

e.g. Disable Watch dog

CLR EA

SETB WDWR

CLR WDE

SETB EA

Table 72. WatchDog and Flash protection byte in Flash (Flash Address = 0x3FFA)

Bit

Location

Bit

Name

Default Value

Description

WDPROT_PROTKY7

This bit holds the protection for the Watchdog timer and the 7th bit of

the Flash protection key.

When this bit is cleared, the watchdog enable and event, selected by

WDE and WDIR cannot be changed by user code. The watchdog

configuration is then fixed to WDIR=0 and WDE=1. The watchdog

timeout in PRE[3:0] can still be modified by user code.

The value of this bit is also used to set the Flash protection key. If this

bit is cleared to protect the watchdog, then the default value for the

Flash protection key is 0x7F instead of 0xFF—see the Protecting the

Flash section for more information on how to clear this bit.

7-0

PROTKY[7:0]

0xFF

These bits hold the flash protection key. The content of this Flash

address is compared to the Flash Protection Key SFR (PROTKY, 0xBB)

when the protection is being set or changed. If the two values match,

the new protection is written to the Flash addresses 0x3FFF to 0x3FFB.

see the Protecting the Flash section for more information on how to

configure these bits.

Watchdog Timer Interrupt

If the watchdog timer is not cleared within the watchdog

timeout period, a system reset will occur unless the watchdog

timer interrupt is enabled. The watchdog timer interrupt enable

bit is located in the WatchDog Timer SFR (WDCON, 0xC0).

Enabling the watchdog timer interrupt allows the program to

examine the stack or other variables that could have led the

program astray. The watchdog timer interrupt also allows the

watchdog to be used as a long interval timer.

Note that the Watchdog Timer Interrupt is automatically

configured as a high priority interrupt. This interrupt cannot be

disabled by the EA bit in the IE register. Even if all of the other

interrupts are disabled, the watchdog is kept active to watch

over the program.

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