M41ST87YMX6TR datasheet(34/54 Pages) STMICROELECTRONICS

34 / 54 page

Clock operation

M41ST87W

34/54

DocID9497 Rev 11

Figure 25: Backup mode alarm waveform

3.5

Watchdog timer

The watchdog timer can be used to detect an out-of-control microprocessor. The user

programs the watchdog timer by setting the desired amount of time-out into the watchdog

bits RB1-RB0 select the resolution, where 00=1/16 second, 01=1/4 second, 10=1 second,

and 11=4 seconds. The amount of time-out is then determined to be the multiplication of

the five-bit multiplier value with the resolution. (For example: writing 00001110 in the

watchdog register = 3*1 or 3 seconds).

Note: The accuracy of the timer is within ± the selected resolution.

If the processor does not reset the timer within the specified period, the M41ST87Y/W sets

the WDF (watchdog flag) and generates either a watchdog interrupt or a microprocessor

reset.

The most significant bit of the watchdog register is the watchdog steering bit (WDS). When

set to a '0,' the watchdog will activate the

IRQ/OUTpinwhentimed-out.WhenWDSisset

to a '1,' the watchdog will output a negative pulse on the

RSTpinfort

rec. The watchdog

when the WDS bit is set to a '1.'

The watchdog timer can be reset by two methods: 1) a transition (high-to-low or low-to-

high) can be applied to the watchdog input pin (WDI) or 2) the microprocessor can perform

a WRITE of the watchdog register. The time-out period then starts over.

Note: The WDI pin should be tied to VSS if not used and is only available in the SOX28

package.

In order to perform a software reset of the watchdog timer, the original time-out period can

be written into the watchdog register, effectively restarting the count-down cycle.

Should the watchdog timer time-out, and the WDS bit is programmed to output an interrupt,

either a transition of the WDI pin, or a value of 00h needs to be written to the watchdog

IRQ/OUTpin.Thiswillalsodisablethewatchdogfunctionuntil

VCC

IRQ/OUT

VPFD

ABE, AFE Bits in Interrupt Register

AF bit in Flags Register

HIGH-Z

VSO

HIGH-Z

trec

M41ST87YMX6TR 数据表(PDF) 34 Page - STMicroelectronics

M41ST87YMX6TR 数据表(HTML) 34 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

数据表下载