NEC 78014Y Series, User Manual

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CHAPTER 20 STANDBY FUNCTION
483
CHAPTER 20 STANDBY FUNCTION
20.1 Standby Function and Configuration
20.1.1 Standby function
The standby function is intended to decrease the power consumption of the system. The following two modes
are available.
(1) HALT mode
HALT instruction execution sets the HALT mode. The HALT mode is intended to stop the CPU operation clock.
System clock oscillator continues oscillation. In this mode, current consumption cannot be decreased as in the
STOP mode. The HALT mode is valid to restart immediately upon interrupt request and to carry out intermittent
operations like watch operations.
(2) STOP mode
STOP instruction execution sets the STOP mode. In the STOP mode, the main system clock oscillator stops
and the whole system stops. CPU current consumption can be considerably decreased.
Data memory low-voltage hold (down to V
DD
= 2 V) is possible. Thus, the STOP mode is effective to hold data
memory contents with ultra-low current consumption.
Because this mode can be cleared upon interrupt request, it enables intermittent operations to be carried out.
However, because a wait time is necessary to secure an oscillation stabilization time after the STOP mode is
cleared, select the HALT mode if it is necessary to start processing immediately upon interrupt request.
In any mode, all the contents of the register, flag and data memory just before standby mode setting are held. The
input/output port output latch and output buffer statuses are also held.
Cautions 1. The STOP mode can be used only when the system operates with the main system clock
(subsystem clock oscillation cannot be stopped). The HALT mode can be used with either the
main system clock or the subsystem clock.
2. When proceeding to the STOP mode, be sure to stop the peripheral hardware operation and
execute the STOP instruction.
3. To decrease power dissipation in A/D converter, clear bit 7 (CS) of A/D converter mode register
(ADM) to 0 and stop the A/D conversion operation before executing the HALT or STOP
instruction.