As far as I know the WDT cannot be disabled in a 1232 supervisor chip. But I am not sure of the IMP 1232. One simple way to feed the 1232 is from the ALE pulse and set the 1232 for maximum time out ( tie TD pin to Vcc) - why not try this ?

Raghu you are absolutly right WatchDog can't be disabled in 1232 supervisors not even in IMP1232 here is the link to datasheet http://www.impweb.com/IMP1232LP.pdf on page 5 it is clearly mentioned that A High-to-low signal trnasition must be regularly issued no latter than the minimum time-out period defined by state of the TD signal Maximum timeout period for this puppy is 1200ms i.e. approx. 1.2seconds not enough for ISP to complete. The only way to use this dog during ISP period is to feed it through ALE. This is the reason why I have started using MAX812 in all my new designs. MAX812 is the most ideal supervisor for P89V51RD2. Follow this link to know more. http://www.8052.com/forum/read.phtml?id=77172

Regards,
Prahlad Purohit