4.12 INTERRUPT CONTROL FLOW (RETI INSTRUCTION)

Figure 4.19 shows the return steps from an interrupt service routine. 8051 CPU saves on an interrupt only the PC (PCH and PCL) onto the stack before start of execution of an interrupt service routine. SFRs, which are expected to be changed at the routine, must be saved by push and must be popped before the last return instruction at the routine.

The 8051 has a return from interrupt instruction as follows: