MC81F4204
April 24, 2012 Ver.1.41 79
A interrupt request is not accepted until the I-flag is set to “1” even if a requested interrupt has higher
priority than that of the current interrupt being serviced. When nested interrupt service is required, the
I-flag should be set to “1” by “EI” instruction in the interrupt service program. In this case, acceptable
interrupt sources are selectively enabled by the individual interrupt enable flags.
Saving/Restoring General-purpose Register
the program status word are automatically saved on the stack, but accumulator and other registers
are not saved itself. These registers are saved by the software if necessary. Also, when multiple
interrupt services are nested, it is necessary to avoid using the same data memory area for saving
registers.
The following method is used to save/restore the general-purpose registers.
Figure 11-2 Timing chart of Interrupt Acceptance and Interrupt Return Instruction
Figure 11-3 Saving/Restoring in Interrupt Routine
To Next Page
Loading...