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Question: What is the difference between a pending interrupt and a posted interrupt?



An interrupt is posted when its interrupt conditions occur. A posted interrupt is not pending unless it is unmasked in the appropriate INT_MSKx register. Disabling an interrupt by clearing its interrupt mask bit (inthe INT_MSKx register) does not clear a posted interrupt, nor does it prevent an interrupt from being posted. It simply prevents a posted interrupt from becoming pending. The picture given below illustrates the Posted Vs Pending interrupt concept. Only the pending interrupts are processed by the Priority Encoder to determine the highest priority interrupt which will be taken by the M8C if the Global Interrupt Enable bit is set in the CPU_F register. For more detail please refer the "Interrupt Controller" section of the TRM.