UPD784021 datasheet(52/90 Pages) NEC

52 / 90 page

mPD784020, 784021

11. STANDBY FUNCTION

The standby function allows the power consumption of the chip to be reduced. The following standby modes are

supported:

• HALT mode : The CPU operation clock is stopped. By occassionally inserting the HALT mode during normal

operation, the overall average power consumption can be reduced.

• IDLE mode : The entire system is stopped, with the exception of the oscillator circuit. This mode consumes

only very little more power than STOP mode, but normal program operation can be restored in

almost as little time as that required to restore normal program operation from HALT mode.

• STOP mode : The oscillator is stopped. All operations in the chip stop, such that only leakage current flows.

These modes can be selected by software.

A macro service can be initiated in HALT mode.

Fig. 11-1 Standby Mode Status Transition

Notes 1. INTP4 and INTP5 are applied when not masked.

2. Only when the interrupt request is not masked

Remark NMI is enabled only by external input. The watchdog timer cannot be used to release one of the standby

modes (STOP or IDLE mode).

STOP

(standby)

IDLE

(standby)

Request for masked interrupt

HALT

(standby)

Set

STOP

RESET

input

Oscillation

settling

time elapses

Wait for

oscillation

settling

Program

operation

Macro service request

End of one operation

End of macro service

Macro

service

UPD784021 Datasheet(PDF) 52 Page - NEC