Interrupt Servicing Operation; Maskable Interrupt Request Acknowledgment Operation - NEC 78K0S/KA1+ Preliminary User's Manual

www.DataSheet4U.com

12.4 Interrupt Servicing Operation

12.4.1 Maskable interrupt request acknowledgment 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 servicing after a maskable interrupt request has been generated is shown in
Table 12-3.
See Figures 12-8 and 12-9 for the interrupt request acknowledgment timing.
www.DataSheet4U.com
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 a status in which it can be acknowledged is set.
Figure 12-7 shows the algorithm of interrupt request acknowledgment.
When a maskable interrupt request is acknowledged, the contents of the 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 servicing, use the RETI instruction.
CHAPTER 12 INTERRUPT FUNCTIONS
Table 12-3. Time from Generation of Maskable Interrupt Request to Servicing
Minimum Time
9 clocks
Note The wait time is maximum when an interrupt
request is generated immediately before BT and
BF instructions.
Remark 1 clock:
Preliminary User's Manual U16898EJ1V0UD
Maximum Time
19 clocks
1
(f : CPU clock)
CPU
f
CPU
Note
221