ST92185B Datasheet, PDF (73/178 Pages) STMicroelectronics – 16K/24K/32K ROM HCMOS MCU WITH ON-SCREEN-DISPLAY

ST92185B - TIMER/WATCHDOG (WDT)
7 ON-CHIP PERIPHERALS
7.1 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.
7.1.1 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 44. Timer/Watchdog Block Diagram
INEN INMD1 INMD2
WDIN¹
INPUT
&
CLOCK CONTROL LOGIC
INTCLK/4
WDTPR
MUX
8-BIT PRESCALER
WDT
CLOCK
WDTRH, WDTRL
16-BIT
DOWNCOUNTER
OUTMD WROUT OUTEN
END OF
COUNT
NMI¹
INT0¹
HW0SW1¹
WDGEN
MUX
IAOS
TLIS
1_{Pin not present on some ST9 devices.}
OUTPUT CONTROL LOGIC
INTERRUPT
CONTROL LOGIC
WDOUT¹
RESET
TOP LEVEL INTERRUPT REQUEST
INTA0 REQUEST
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