Lpc2000

Hi,

I was viewing the schematic for a LPC2106 based design (see 
http://www.mct.net/product/dil2106/schema.pdf). It included a NPC303 
external watchdog chip. Is this needed if we are not running our 
design off batteries?

Regards,
Shane.

It depends what your reliability requirements are.

The internal watchdog is disabled at reset, and the WDTC register can 
be written to at any time (writing a large value to this register 
effectively disable the watchdog by making the timeout period in the 
minutes range), so if you need a reliable watchdog you should 
consider adding an external one.


--- In lpc2000@yahoogroups.com, "smt5211" <from-yahoo@d...> wrote:
> 
> Hi,
> 
> I was viewing the schematic for a LPC2106 based design (see 
> http://www.mct.net/product/dil2106/schema.pdf). It included a 
NPC303 

> external watchdog chip. Is this needed if we are not running our 
> design off batteries?
> 
> Regards,
> Shane.

Hi,

Totally agree, one more additional point. If you loose your clock
(crystal breaks or something like it), the micro will freeze with the
outputs in the respective states. An external watchdog or an internal
oscillator for the watchdog can get the outputs into reset state,
which is input and they would not drive some high current power
transistors for an extended period of time. 

Overall the watchdog is good enough as "software watchdog" but still
reseting it or setting it to a very high value is a little to easy if
you need high reliability.

Cheers, Bob

--- In lpc2000@yahoogroups.com, "lp2000c" <lp2000c@e...> wrote:

> 
> It depends what your reliability requirements are.
> 
> The internal watchdog is disabled at reset, and the WDTC register can 
> be written to at any time (writing a large value to this register 
> effectively disable the watchdog by making the timeout period in the 
> minutes range), so if you need a reliable watchdog you should 
> consider adding an external one.
> 
> 
> --- In lpc2000@yahoogroups.com, "smt5211" <from-yahoo@d...> wrote:
> > 
> > Hi,
> > 
> > I was viewing the schematic for a LPC2106 based design (see 
> > http://www.mct.net/product/dil2106/schema.pdf). It included a 
> NPC303 
> > external watchdog chip. Is this needed if we are not running our 
> > design off batteries?
> > 
> > Regards,
> > Shane.