Kelvin,

Some 8051s come with internal watchdog timers and from a previous discussion I recall that some of us prefer external watchdogs even so.

We recently discussed the pros and cons and I realized that doing FLASH in ISP mode could be a problem with an external watchdog; it would timeout and reset the micro while it was burning FLASH.

Wednesday I figured out an nice solution and am awaiting a confirmation from one of the chip manufacturers I buy from.

Hopefully, they'll agree to nail down the current characterists into the specifications for future releases. It would be easy for one of their designers to change this particular aspect thinking it affects nothing.

If they say its always going to behave that way, I'll share the trick.

-Jay C. Box