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User’s Manual U15104EJ2V0UD
CHAPTER 15 STANDBY FUNCTION
15.1 Standby Function and Configuration
15.1.1 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 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 such as in watch applications.
Although the CPU stops operating, the peripheral functions can operate. To lower the current consumption,
therefore, stop all unnecessary circuits before executing the HALT instruction.
(2) STOP mode
STOP instruction execution sets the STOP mode. In the STOP mode, the 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
= 2.2 V) is possible. Thus, the STOP mode is effective to hold
data memory contents with ultra-low current consumption.
If the supply voltage drops below 2.2 V, the system is reset by means of power-on clear reset. For reset, refer
to CHAPTER 16 RESET FUNCTION.
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.
All the functions stop operating.
Some registers of the PLL frequency synthesizer and frequency counter are reset, but the other functions are
stopped with their current status retained.
Cautions 1. When shifting to the STOP mode, be sure to stop the peripheral hardware operation
before executing the STOP instruction.
2. The following sequence is recommended for power consumption reduction of the A/D
converter: first clear bit 7 (ADCS3) of ADM3 to 0 to stop the A/D conversion operation,
then execute the HALT or STOP instruction.
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