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TIMER/WATCHDOG (WDT)

10 ON-CHIP PERIPHERALS

10.1 TIMER/WATCHDOG (WDT)

Important Note: This chapter is a generic descrip-

tion of the WDT peripheral. However depending

on the ST9 device, some or all of WDT interface

signals described may not be connected to exter-

nal pins. For the list of WDT pins present on the

ST9 device, refer to the device pinout description

in the first section of the data sheet.

10.1.1 Introduction

The Timer/Watchdog (WDT) peripheral consists of

a programmable 16-bit timer and an 8-bit prescal-

er. It can be used, for example, to:

– Generate periodic interrupts

– Measure input signal pulse widths

– Request an interrupt after a set number of events

– Generate an output signal waveform

– Act as a Watchdog timer to monitor system in-

tegrity

The main WDT registers are:

– Control register for the input, output and interrupt

logic blocks (WDTCR)

– 16-bit counter register pair (WDTHR, WDTLR)

– Prescaler register (WDTPR)

The hardware interface consists of up to five sig-

nals:

– WDIN External clock input

– WDOUT Square wave or PWM signal output

– INT0 External interrupt input

– NMI Non-Maskable Interrupt input

– HW0SW1 Hardware/Software Watchdog ena-

ble.

Figure 87. Timer/Watchdog Block Diagram

INT0

INPUT

CLOCK CONTROL LOGIC

INEN INMD1 INMD2

WDTPR

8-BIT PRESCALER

WDTRH, WDTRL

16-BIT

INTCLK/4

WDT

OUTMD

WROUT

OUTPUT CONTROL LOGIC

INTERRUPT

CONTROL LOGIC

END OF

COUNT

RESET

TOP LEVEL INTERRUPT REQUEST

OUTEN

MUX

WDOUT

IAOS

TLIS

INTA0 REQUEST

NMI

WDGEN

HW0SW1

WDIN

MUX

DOWNCOUNTER

CLOCK

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