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User’s Manual U14260EJ3V1UD
CHAPTER 21 STANDBY FUNCTION
21.1 Standby Function and Configuration
21.1.1 Standby function
The standby function is designed to decrease power consumption of the system. The following two modes are
available.
(1) HALT mode
HALT instruction execution sets the HALT mode. The HALT mode stops the CPU operation clock. If the main
system clock oscillator or subsystem clock oscillator is operating before the HALT mode is set, oscillation of each
clock continues. In this mode, power consumption is not decreased as much as in the STOP mode. However,
the HALT mode is effective to restart operation immediately upon an interrupt request and to carry out intermittent
operations.
(2) STOP mode
STOP instruction execution sets the STOP mode. In the STOP mode, the main system clock oscillator stops,
stopping the whole system, thereby considerably reducing the CPU power consumption.
Data memory low-voltage hold (down to V
DD
= 1.6 V) is possible. Thus, the STOP mode is effective to hold data
memory contents with ultra-low power consumption.
Because this mode can be released upon an interrupt request, it enables intermittent operations to be carried
out. However, because a wait time is required to stabilize oscillation after the STOP mode is released, select
the HALT mode if it is necessary to start processing immediately upon an interrupt request.
In either of these two modes, all the contents of registers, flags and data memory just before the standby mode
is set are held. The I/O port output latches 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 operation is transferred to the STOP mode, be sure to stop operation of the peripheral
hardware operating with the main system clock before executing the STOP instruction.
3. The following sequence is recommended for reducing the power consumption of the A/D
converter when the standby function is used: First clear bit 7 (ADCS0) of A/D converter mode
register 0 (ADM0) to 0 to stop the A/D conversion operation, and then execute the HALT or
STOP instruction.