The 89C51 has an additional PCA interrupt.
The priority mechanism is also different compared to a normal 8051.
You can set a level in the range from 0-3.
PRIORITY SET|RESET source , level
level can be 0,1,2 or 3.(0=lowest,3=highest)
The source can be :
PRIORITY SET INT0,3 'will set INT0 to the highest priority.
Look at a datasheet for more details.
The WATCHDOG can be started with the statement :
RESET WATCHDOG must be used in your program to reset the WD-timer.
When it reaches 16384 the chip will be reset.
The input to the WD-timer is the XTAL frequency!