Often I use serial port expansion, because easier pcb (less wires) and no limitation.

Then I feed the inverted output enable to the 8051 and depending from the wanted default state I connect pullup or pulldown resistors on the outputs.

So during reset the output stages are disabled and the wanted default output level was present on all outputs.

After reset, the 8051 load new data in and put the output enable to low (all output stages on).

So also on a watchdog reset the safe default state was entered automatically.


Peter