Electronics America Single-Chip Microcontrollers User's Manual

CHAPTER 16 INTERRUPT FUNCTIONS
User’s Manual U15331EJ4V1UD 305
Figure 16-16. Example of Multiple Interrupt Servicing
Example 1. Acknowledging multiple interrupts
INTyy
EI
Main servicing
EI
INTyy servicingINTxx servicing
RETI
IE = 0
INTxx
RETI
IE = 0
The interrupt request INTyy is acknowledged during the servicing of interrupt INTxx and multiple interrupts are
performed. Before each interrupt request is acknowledged, the EI instruction is issued and the interrupt request is
enabled.
Example 2. Multiple interrupt servicing is not performed because interrupts are disabled
INTyy
EI
Main servicing
RETI
INTyy servicingINTxx servicing
IE = 0
INTxx
RETI
INTyy is held pending
IE = 0
Because interrupt requests are disabled (the EI instruction has not been issued) in the INTxx interrupt servicing,
the interrupt request INTyy is not acknowledged and multiple interrupt servicing is not performed. INTyy is held
pending and is acknowledged after INTxx servicing is completed.
IE = 0: Interrupt requests disabled