
CHAPTER 13 STANDBY FUNCTION
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CHAPTER 13 STANDBY FUNCTION
13.1 Standby Function and Configuration
13.1.1 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.
The system clock oscillator continues oscillating. In this mode, the 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 clock 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. The 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 the 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. When proceeding to the STOP mode, be sure to stop the peripheral hardware operation and
execute the STOP instruction.
2. In order to decrease the power consumption in the A/D converter, clear bit 7 (CS0) in the A/
D converter mode register (ADM0) to 0 and stop A/D conversion operation before executing
a HALT or STOP instruction.