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7.3 Maskable Interrupts
Maskable interrupt requests can be masked by interrupt control registers. The V850E/IA1 has 52 maskable
interrupt sources.
If two or more maskable interrupt requests are generated at the same time, they are acknowledged according to
the default priority. In addition to the default priority, eight levels of priorities can be specified by using the interrupt
control registers (programmable priority control).
When an interrupt request has been acknowledged, the acknowledgement of other maskable interrupt requests is
disabled and the interrupt disabled (DI) status is set.
When the EI instruction is executed in an interrupt servicing routine, the interrupt enabled (EI) status is set, which
enables servicing of interrupts having a higher priority than the interrupt request in progress (specified by the
interrupt control register). Note that only interrupts with a higher priority will have this capability; interrupts with the
same priority level cannot be nested.
However, if multiple interrupts are executed, the following processing is necessary.
<1> Save EIPC and EIPSW in memory or a general-purpose register before executing the EI instruction.
<2> Execute the DI instruction before executing the RETI instruction, then reset EIPC and EIPSW with the values
saved in <1>.
7.3.1 Operation
If a maskable interrupt occurs by INT input, the CPU performs the following processing, and transfers control to a
handler routine.
(1) Saves the restored PC to EIPC.
(2) Saves the current PSW to EIPSW.
(3) Writes an exception code to the lower halfword of ECR (EICC).
(4) Sets the ID bit of the PSW and clears the EP bit.
(5) Sets the handler address corresponding to each interrupt to the PC, and transfers control.
The servicing configuration of a maskable interrupt is shown in Figure 7-4.
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CHAPTER 7 INTERRUPT/EXCEPTION PROCESSING FUNCTION
User's Manual U14492EJ3V0UD
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