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ST9 USER GUIDE

/* *********** Configure Watchdog for Periodic Interrupt *************/

void ConfigWDT ( void )

{

SelectPage( WDT_PG )

;/* select Watchdog page */

WDTPR = 0 ;/* 122 us = 366 ticks */

WDTR = 365 ;/* preset is nb ticks-1 (WDTR is the pair WDTLR and WDTHR) */

WDTCR = (WDTm_stsp) ;/* WDT is set to continuous mode, no inputs, no

outputs */

/* Interrupt must be connected to intA0 in the EIVR register */

}

The initialisation routine for INTA0 follows. In this example application, interrupt A0 is the only

"external" interrupt enabled, and it is assigned priority level 2:

/* ***********Initialise Interrupt A0 and Current Level **************/

void ConfigInterrupts ( void )

{

SelectPage( EXINT_PG ) ;

EIVR = (EIm_tlism+(unsigned char)INTA0VECT) ;/* int. A0 is generated

on WDT overflow */

EIPLR = 1 ;/* intr A0 (and that of same group) with high priority */

EIMR = EIm_ia0m ;/* intr A0 alone enabled */

CICR = (Im_gcenm+Im_iamm+Im_ienm)+7 ;

/* current processing level: minimum ; int. enabled, nested mode */

/* This starts also the MFT */

}

4.3.3 Watchdog Application 1: Generating a PWM

This application provides a PWM with a programmable duty cycle. You can use it as an appli-

cation exercise for learning to use the programming and debugging tools since it is very

simple. The only hardware required to watch the effect of the program is a LED in series with

a resistor connected between P4.4 and Vcc (anode towards Vcc). You will find the application

in the Companion software in the WDT/appli1 directory.

The WDT can only provide a delay after which the output may change its state, and an inter-

rupt is triggered. The principle of using the WDT as a rectangular signal generator is to set it

to Continuous mode, to load it with a time value, and let it count down until zero. The control

time. The interrupt service routine will reload with the other value, and preset the WROUT bit

to the complement of the current value, so that the opposite state will be transferred to the

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