PD17225_15 Datasheet, PDF (42/86 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLER FOR SMALL GENERAL-PURPOSE INFRARED REMOTE CONTROL TRANSMITTER

µPD17225, 17226, 17227, 17228
7. INTERRUPT FUNCTIONS
7.1 Interrupt Sources
µPD17225 is provided with three interrupt sources.
When an interrupt has been accepted, the program execution automatically branches to a predetermined address,
which is called a vector address. A vector address is assigned to each interrupt source, as shown in Table 7-1.
Table 7-1. Vector Address
Priority
1
2
3
Interrupt Source
8-bit timer
INT pin rising and falling edges
Basic interval timer
Ext/Int
Internal
External
Internal
Vector Address
0003H
0002H
0001H
When more than one interrupt request is issued at the same time, the interrupts are accepted in sequence, starting
from the one with the highest priority.
Whether an interrupt is enabled or disabled is specified by the EI or DI instruction. The basic condition under which
an interrupt is accepted is that the interrupt is enabled by the EI instruction. While the DI instruction is executed, or while
an interrupt is accepted, the interrupt is disabled.
To enable accepting an interrupt after the interrupt has been processed, the EI instruction must be executed before
the RETI instruction. Accepting the interrupt is enabled by the EI instruction after the instruction next to the EI instruction
has been executed. Therefore, no interrupt can be accepted between the EI and RETI instructions.
Caution In interrupt processing, only the BCD, CMP, CY, Z, IXE flags are automatically saved to the stack
by the hardware, to a maximum of three levels. Also, within the interrupt processing contents, when
peripheral hardware (timer, A/D converter, etc. ) is accessed, the DBF and WR contents are not saved
by the hardware. Accordingly, it is recommended that at the beginning of interrupt processing DBF
and WR be saved by software to RAM, and immediately before finishing interrupt processing the
saved contents be returned to thier original location.
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Data Sheet U12643EJ2V0DS00