NEC PD78P214 Manuale Utente

380

µ

PD78214 Sub-Series

HALT mode can be released by any of the following three sources:

• Nonmaskable interrupt request (NMI)

• Maskable interrupt request (vectored interrupt or macro service)

• RESET input

Table 14-2 lists the sources used for releasing HALT mode and the operations that are performed after HALT mode
is released by each source.

Operation

Ordinary reset operation

Releasing source

MK

××

RESET input

Nonmaskable

interrupt request

Maskable

vectored interrupt

request

×

0

0

0

0

0

1

PR

××

IE

ISP

×

×

1

×

1

0

×

×

1

1

0

0

×

×

×

0

×

0

×

1

×

Handling a vectored interrupt

Executing the macro service

When the end conditions are satisfied, a vectored interrupt

is handled.

When the end conditions are not satisfied, HALT mode is

resumed.

Macro service

request

—

×

×

—

Executing the instruction at the next address (holding the

interrupt request)

Executing the macro service

When the end conditions are satisfied, the instruction at the

next address is executed.

When the end conditions are not satisfied, HALT mode is

resumed.

Executing the macro service then resuming HALT mode

(holding the interrupt request)

Continuing HALT mode

0

0

0

0

0

1

1

1

0

0

×

×

0

×

0

×

1

×

×

1

×

1

0

×

Continuing HALT mode (holding the interrupt request)

Handling a vectored interrupt

Note When the NMIS bit of the interrupt status register (LST) is set to 1, the instruction at the next address is executed.  Processing then

branches to the NMI interrupt service program when NMIS is cleared to 0.

Remark MK

×× : Interrupt mask flag

PR

×× : Priority designation flag

IE

: Interrupt request enable flag

ISP

: Interrupt priority status flag

When a nonmaskable interrupt (NMI) is requested, HALT mode is released regardless of whether interrupts
are enabled (EI) or disabled (DI).

Once HALT mode has been released, processing branches to the NMI service program if the NMIS bit of the
interrupt status register (IST) is set to 0.  If the NMIS bit is set to 1 (for example, when HALT mode is specified
in the NMI interrupt service program), processing is resumed from the instruction subsequent the one that
has specified HALT mode.  Processing then branches to the NMI interrupt service program when the NMIS
bit is set to 0 (for example, with a RETI instruction).