L9908 datasheet(131/152 Pages) STMICROELECTRONICS

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Table 145. Watchdog configuration table for WDT overflow timer

WDT_OVF_CFG1

WDT_OVF_CFG0

Description

11.26 ms

22.52 ms (Default)

45.04 ms

90.11 ms

The WDT overflow counter status can be accessed through the dedicated SPI read only register

WDT_OVF_STATUS.

The counter value in seconds can be retrieved by the following reconstruction formula:

TWTD_OVF−STATUS=ΔWTD_OVF_LSB×DWTD_OVF_STATUS

(27)

Where: DWDT_OVF is the digital word stored in WDT_OVF_STATUS and ∆WDT_OVF_LSB is the counter LSB as

defined in Table 146.

Table 146. WDT overflow timer LSB

WDT_OVF_CFG

Description

0.2048 ms

0.4096 ms (Default)

0.8192 ms

1.6384 ms

Reprogramming of WDT_OVF_CFG configuration is possible only while WDT_EN = 0

Table 147. WDT overflow counter accuracy

Symbol

Parameter

Min

Typ

Max

Unit

WDT_ovf_acc

WDT overflow counter accuracy

-10

Within this window the watchdog expects a refresh pulse to reset the overflow counter and restart a new window:

if refresh is missed before the overflow counter is elapsed the error flag WDT_OVF_Fail is set and L9908 is sent

to safe state. The flag remains set until the WDT is reset by the SPI command or re-enabled after a power-on

sequence.

Figure 86. WDT operation – Overflow timer failure

L9908

Functional description

DS13546 - Rev 5

page 131/152

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