NEC mPD789101, User Manual

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CHAPTER 15 INTERRUPT FUNCTIONS
User’s Manual U13045EJ2V0UM00
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15.4.2 Maskable interrupt request acknowledgement operation
A maskable interrupt request can be acknowledged when the interrupt request flag is set to 1 and the corresponding
interrupt mask flag is cleared to 0. A vectored interrupt request is acknowledged in the interrupt enabled status (when
the IE flag is set to 1).
The time required to start the interrupt processing after a maskable interrupt request has been generated is shown
in Table 15-3.
Refer to Figures 15-10 and 15-11 for the interrupt request acknowledgement timing.
Table 15-3. Time from Generation of Maskable Interrupt Request to Processing
Minimum Time Maximum Time
Note
9 clocks 19 clocks
Note The wait time is maximum when an
interrupt request is generated immediately
before BT and BF instruction.
Remark 1 clock: (f
CPU
: CPU clock)
When two or more maskable interrupt requests are generated at the same time, they are acknowledged starting
from the interrupt request assigned the highest priority.
A pending interrupt is acknowledged when the status where it can be acknowledged is set.
Figure 15-9 shows the algorithm of acknowledging interrupt requests.
When a maskable interrupt request is acknowledged, the contents of PSW and PC are saved to the stack in that
order, the IE flag is reset to 0, and the data in the vector table determined for each interrupt request is loaded to the
PC, and execution branches.
To return from interrupt processing, use the RETI instruction.
1
f
CPU