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HD407L4818H

4-Bit Single-Chip Microcomputer

Renesas Electronics 

HD404818 Series

Interrupts

Six interrupt sources are available on the MCU: external requests (INT0, INT1), timer/counters (timers A,

B, and C), and the serial interface. For each source, an interrupt request flag (IF), interrupt mask (IM), and

interrupt vector addresses are provided to control and maintain the interrupt request. The interrupt enable

flag (IE) is also used to control interrupt operations.

Interrupt Control Bits and Interrupt Servicing: The interrupt control bits are mapped on $000 through

$003 by the RAM space. They are accessible by RAM bit manipulations instructions, although the interrupt

request flag (IF) cannot be set by software. The interrupt enable flag (IE) and IF are cleared to 0, and the

interrupt mask (IM) is set to 1 after MCU reset.

Figure 6 is a block diagram of the interrupt control circuit. Table 2 shows the interrupt priority and vector

addresses, and table 3 shows the interrupt conditions corresponding to each interrupt source.

The interrupt request is generated when IF is set to 1 and IM is 0. If IE is 1 at this time, the interrupt will be

activated and vector addresses will be generated from the priority PLA corresponding to the interrupt

sources.

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