ST92141 datasheet(164/179 Pages) STMICROELECTRONICS

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ST92141 - ELECTRICAL CHARACTERISTICS

WATCHDOG TIMING TABLE

(VDD = 5V ± 10%, TA = –40°C to +85°C, CLoad = 50pF, fINTCLK = 25MHz, Push-pull output configuration,

unless otherwise specified)

Note: The value in the left hand column shows the formula used to calculate the timing minimum or maximum from the oscillator clock period,

watchdog prescaler and counter programmed values.

The value in the right hand two columns show the timing minimum and maximum for an internal clock (INTCLK) at 25MHz, with minimum and

maximum prescaler value and minimum and maximum counter value.

Measurement points are taken with reference to VIH-VIH / VOH-VOH for positive pulse and VIL-VIL / VOL-VOL for negative pulse

(1) Formula guaranteed by design.

Legend:

Tck = INTCLK period = OSCIN period when OSCIN is not divided by 2;

2 x OSCIN period when OSCIN is divided by 2;

OSCIN period x PLL factor when the PLL is enabled.

Psc = Watchdog Prescaler Register content (WDTPR): from 0 to 255

Cnt = Watchdog Counter Registers content (WDTRH,WDTRL): from 0 to 65535

TWDIN = Watchdog Input signal period (WDIN)

WATCHDOG TIMING

N°

Symbol

Parameter

Value (Note)

Unit

Formula(1)

Min

Max

TwWDOL

WDOUT Low Pulse Width

4 x (Psc+1) x (Cnt+1) x Tck

160

2.69

(Psc+1) x (Cnt+1) x TWDIN

with TWDIN ≥ 8 x Tck

320

TwWDOH

WDOUT High Pulse Width

4 x (Psc+1) x (Cnt+1) x Tck

160

2.69

(Psc+1) x (Cnt+1) x TWDIN

with TWDIN ≥ 8 x Tck

320

TwWDIL

WDIN High Pulse Width

≥ 4 x Tck + 10

170

TwWDIH

WDIN Low Pulse Width

≥ 4 x Tck +10

170

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