HD6475348R Datasheet, PDF (109/487 Pages) Hitachi Semiconductor – Single-Chip Microcomputer

The on-chip interrupt controller decides whether an interrupt can be accepted by comparing its
priority with the interrupt mask level, and determines the order in which to accept competing
interrupt requests. Interrupts that are not accepted immediately remain pending until they can be
accepted later.
When it accepts an interrupt, the interrupt controller also decides whether to interrupt the CPU or
start the on-chip data transfer controller (DTC). This decision is controlled by bits set in four data
transfer enable registers (DTEA to DTEF) in the register field. The DTC is started if the
corresponding bit in DTEA to DTEF is set to 1; otherwise a CPU interrupt is generated. DTC
interrupts provide an efficient way to send and receive blocks of data via the serial communication
interface, or to transfer data between memory and I/O without detailed CPU programming. The
CPU stops while the DTC is operating. DTC interrupts are described in section 6, “Data Transfer
Controller.”
The hardware exception-handling sequence for a CPU interrupt clears the T bit in the status register to
0 and sets the interrupt mask level in bits I2 to I0 to the level of the interrupt it has accepted. This
prevents the interrupt-handling routine from being interrupted except by a higher-level interrupt. The
previous interrupt mask level is restored on the return from the interrupt-handling routine.
For further information on interrupts, see section 5, “Interrupt Controller.”
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