Lpc2000

I've been using an external 8-pin micro as a reset/watchdog control for 
years. Originally I used the PIC12C509 and more recently the 12C629 as 
they have proved very reliable. Even the LPC903, albeit in SMD. Use the 
internal RC oscillator, apply VDD and presto. The watchdog can be a 
smart watchdog that requires a serial bit stream to start it up and 
continue to activate it or whatever you like.

But I never waste resources as this micro always monitors my main coms 
receive line and allows me to remotely reset, stop, or place the host 
micro in bootload mode. Back in the nineties I was guilty of using AVRs 
which did not have any internal boot code but could be Flash programmed 
via an SPI like interface. So the external reset micro would be kind 
enough to receive an intel hex file and burn it in line by line, all 
over a 3-wire serial interface. Of course, I use them on my LPC2000s as 
well.

One reason I like the 8-pin DIP format is for that reason ... DIP, as 
everything else tends to be smd I can still burn my special watchdog 
chip externally and then plug it in. I even code serial numbers in these 
little suckers. I have yet to make one of these lock-up or even glitch.

There you go, combo reset/watchdog/ISP/serial# chip, all for a buck.

..and yes, I have waxed lyrical about this once or twice before.

my2cents
*Peter*

Robert Adsett wrote:

>At 12:04 AM 10/18/05 +0200, Sten wrote:
>  
>
>>lhaddix wrote:
>>    
>>
>>>I guess as Marcio points out the larger issue is why are there
>>>situations where the internal watchdog can't reset the micro.
>>>Unfortunately this is probably a feature of the LPC design.
>>>
>>>Microchip uses an internal RC for thier watchdog which is not
>>>dependant of the system clock for instance.
>>>
>>>I think what happens is it's possible for an ESD hit to stop
>>>the crystal osc on the LPC such that reset is needed to restart
>>>the oscillator, but there can be no watchdog reset without a system
>>>clock.
>>>
>>>I've considered using an external osc to feed the ARM, but don't
>>>wish to do this. I can't be sure it would fix the problem without
>>>mocking it up and then blasting with the static gun, but I know that
>>>toggling reset from outside will restart the clock.
>>>
>>>Landrum
>>>
>>>      
>>>
>>I had some similar problems with a LPC2124 last year. During ESD test
>>the LPC stops with and without internal watchdog. But we had another
>>(bigger) MCU on our board which was able to turn off/turn on the LPC if
>>it didn't response to hello-request packet in such a case.
>>    
>>
>
>
>I think the additional micro as watchdog is not a bad idea.  A little 8 pin 
>micro can act as quit a flexible watchdog.  1 pin for reset, 1 as the 
>watchdog input, a couple to check for various startup or runtime 
>conditions.  If it has a good reliable power monitor built in even 
>better.  It' may even be cost competitive with a windowed watchdog.
>
>Jack Ganselle has an article where he waxes rhapsodic about the possibilities.
>
>Robert
>  
>