XC888LM datasheet(88/144 Pages) INFINEON

88 / 144 page

XC886/888CLM

Functional Description

Data Sheet

V0.9, 2006-12

If the WDT is not serviced before the timer overflow, a system malfunction is assumed.

As a result, the WDT NMI is triggered (assert FNMIWDT) and the reset prewarning is

entered. The prewarning period lasts for 30

H count, after which the system is reset

(assert WDTRST).

The WDT has a “programmable window boundary” which disallows any refresh during

the WDT’s count-up. A refresh during this window boundary constitutes an invalid

access to the WDT, causing the reset prewarning to be entered but without triggering the

WDT NMI. The system will still be reset after the prewarning period is over. The window

boundary is from 0000

H to the value obtained from the concatenation of WDTWINB and

After being serviced, the WDT continues counting up from the value (<WDTREL> * 2

8).

The time period for an overflow of the WDT is programmable in two ways:

•

The input frequency to the WDT can be selected to be either

PCLK/2 or fPCLK/128

•

The reload value WDTREL for the high byte of WDT can be programmed in register

WDTREL

The period,

WDT, between servicing the WDT and the next overflow can be determined

by the following formula:

(3.4)

If the Window-Boundary Refresh feature of the WDT is enabled, the period

WDT

between servicing the WDT and the next overflow is shortened if WDTWINB is greater

than WDTREL, see Figure 29. This period can be calculated using the same formula by

replacing WDTREL with WDTWINB. For this feature to be useful, WDTWINB cannot be

smaller than WDTREL.

WDT

2 1WDTIN

()

216

WDTREL

–

()

PCLK

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