internal watchdog

[ramabh]

Hi

I am working on Freescale HCS08 microcontroller.

and i am using internal watchdog provided by it ,Datasheet says its refresh time is 32msec but when i checked through CRO it showed me 37msec.Is there any chance that at cold temperatures it will take more time than that.

[bigmac]

Hello,

You do not say which HCS08 device you are using.  The variation of COP timeout period will depend entirely on the oscillator source that increments the COP counter.  If an internal RC oscillator is used, this will generally have a wide frequency tolerance unit-to-unit, and for variation of voltage and temperature.

Normally the minimum interval is the critical period because it determines how frequently COP counter reset must occur to prevent timeout.

Regards,

Mac

[ramabh]

Hi

i am using MC9S08DZ60 microcontroller.

With your message it is clear that with temperature even internal watchdog timeout period will increase.

I mentioned watchdog time out period to be 32msec but its varying between 32 to 40msec,Is there any chance that at cold temperatures like -40 the timeout will increaase more than 50msec

[bigmac]

Hello,

According to the data sheet for the DZ60, the internal low power oscillator may have a period between the limits 0.7 to 1.3 milliseconds.  When this is used as the source for the COP timer, and using the shortest threshold setting, the COP timeout period should lie somewhere between 22 and 42 ms.  Since there doesn't appear to be a published temperature curve for the oscillator, it is unclear whether these limits would apply over the full range of temperatures.

If it is important for your application that the COP timeout period be more closely controlled, you will need to alternatively consider the bus frequency as the COP timeout source.  Refer to table 5.6 in the data sheet.

Regards,

Mac