Hi Rustu,

it seems, you came from the PIC world, where separate stacks used for interrupts and subroutines or data. Yes on such architecture there is no way to implement different interrupt priorities.

But on the 8051 there is no separate stack and interrupts are working like calls and so also interrupts can be interrupted.

Some 8051 derivates (e.g. T89C51RD2) can also use up to four interrupt priorities. Since any interrupt pushes its own return address onto the stack, up to 8 bytes of the stack can be utilized in this case.
Additional stack utilization can occur, if some registers must be preserved inside the interrupts.


Peter