Anil:
I think you are nuts. You better look at the prices for the watchdog/reset generators. You will find the chips almost the same price in quantity. Particularly if you were to just focus on reset generators. On top of that I think you have totally missled yourself about the cost. The chip cost is only part of the cost within a product. You need to add the costs of all the additional components needed around your silly pair of 555 chips. Even you admitted the need for MOSFETS and extra CAPACITORS for AC coupling. Also add the costs for managing an extra 5 or 10 line items on the BOM including purchasing and inventory processing. Also add the cost for additional PC board space plus hole drilling if through hole is used. Add the cost of labor to install these extra components. Add the cost to test this circuit, particulary the products where the wrong components are installed incorrectly.

When you total those costs all up you will see the single chip watch dog wins hands down EVERY time.

OK OK I appologize. It is ok to tell us about your past experience of what you may have once done. But it is my opinion that it is rediculous to defend this type of design as "555 is very cheap & reliable & ready available and so can be a very good option for processors not having internal WD".

Michael Karas