RM0319 datasheet(348/368 Pages) STMICROELECTRONICS

348 / 368 page

Watchdog timer (WDT)

RM0319

348/368

Doc ID 022640 Rev 3

Figure 115. Watchdog module block diagram

34.3.1

AMBA APB interface

The AMBA APB interface block provides an APB slave which allows to accesses to all

registers in the watchdog module.

In particular, the lock register (WdogLock) controls the enabling of write accesses to all the

other registers in order to ensure software cannot unintentionally disable the watchdog

module operation.

34.3.2

Free running counter

The free running counter block contains the 32-bit down counter functionality (including

related registers), and the logic to generate the interrupt and reset signal outputs.

The counter and the interrupt/reset logic are clocked independently, as detailed in

Section 34.4 on page 348.

34.4

Clocks

The watchdog module uses two different input clocks:

●

The clock of the APB bus (PCLK signal), which is used to clock the Watchdog module

registers through APB bus.

●

The external WDOGCLK signal which, in conjunction with its clock enable,

WGDOGCLKEN, is used to clock the Watchdog module counter and its associated

interrupt and reset generation logic. In particular, the watchdog counter only

decrements on a rising edge of WDOGCLK when WDOGCLKEN is HIGH.

The following constraints must be observed in the relationship between the two clocks:

●

The rising edge of WDOGCLK must be synchronous and balanced with the rising edge

of PCLK,

●

The WDOGCLK frequency cannot be greater than the PCLK frequency.

From the constraints above and depending on the relationship between WDOGCLK and

WDOGCLKEN, the watchdog module counter is decremented on different ways

summarized in Table 123.

Free Running

Counter

Load Register Control Register

32-bit down counter

Value Register

Interrupt and

Reset generation

Raw Interrupt Status Register

Masked Interrupt Status Register

Interrupt Clear Register

AMBA APB Interface

ID Registers

Lock Register

Integration Test Register

WDOGINT

WDOGRES

AMBA APB

Signals

WDOGCLK

WDOGCLKEN

WDOGRESn

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