Hi,

The last post was related to generic 80C51, what the standard implementation is.
Different vendors may have implemented the reset circuitry differently.
Some newer 80C51s (P87LPC76x, P89LPC9xx) have a POR circuit (power on reset) , which gives a reset signal on power up of the device. This will put the port SFRs in the (defined) Reset state.
The POR will generate a reset on power-up, then the part does not have to wait till the oscillator has started up to provide a valid reset, as on generic 80C51s.

The reset circuitry is a gray area, it varies from different parts and from different vendors.

Regards,

Bauke