CHAPTER 18 STANDBY FUNCTION
321
CHAPTER 18 STANDBY FUNCTION
18.1 Standby Function and Configuration
18.1.1 Standby function
The standby function is intended 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 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 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. CPU current consumption can be considerably decreased.
Data memory low-voltage hold (down to VDD = 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 released by an
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 released, select the HALT mode if it is necessary to start processing immediately by using an interrupt
request.
In any modes, 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.
When proceeding to the STOP mode, be sure to stop the peripheral hardware operation
and execute the STOP instruction.
In consideration of power consumption reduction at the A/D converter, set bit 7 (CS)
of the A/D converter mode register (ADM) register to 0 to stop the A/D converter's
operation before executing the HALT or STOP instruction.
2.
3.