Datasheet

78K0/Ix2 CHAPTER 19 STANDBY FUNCTION
R01UH0010EJ0500 Rev.5.00 600
Feb 28, 2012
CHAPTER 19 STANDBY FUNCTION
19.1 Standby Function and Configuration
19.1.1 Standby function
T
he standby function is mounted onto all 78K0/Ix2 microcontroller products.
The standby function is designed to reduce the operating current of the system. The following two modes are available.
(1) HALT mode
HALT instruction execution sets the HALT mode. In the HALT mode, the CPU operation clock is stopped. If the high-
speed system clock oscillator, internal high-speed oscillator, or internal low-speed oscillator is operating before the
HALT mode is set, oscillation of each clock continues. In this mode, the operating current is not decreased as much
as in the STOP mode, but the HALT mode is effective for restarting operation immediately upon interrupt request
generation and carrying out intermittent operations frequently.
(2) STOP mode
STOP instruction execution sets the STOP mode. In the STOP mode, the high-speed system clock oscillator and
internal high-speed oscillator stop, stopping the whole system, thereby considerably reducing the CPU operating
current.
Because this mode can be cleared by an interrupt request, it enables intermittent operations to be carried out.
However, because a wait time is required to secure the oscillation stabilization time after the STOP mode is released
when the X1 clock is selected, select the HALT mode if it is necessary to start processing immediately upon interrupt
request generation.
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. When shifting to the STOP mode, be sure to stop the peripheral hardware operation operating
with main system clock before executing STOP instruction.
2. When transitioning to the STOP mode, it is possible to achieve low power consumption by
setting RMC = 56H.
3. The following sequence is recommended for operating current reduction of the A/D converter
when the standby function is used: First clear bit 7 (ADCS) and bit 0 (ADCE) of the A/D converter
mode register 0 (ADM0) to 0 to stop the A/D conversion operation, and then execute the STOP
instruction.
4. Stop the operational amplifier and comparator before executing the STOP instruction.