545CHAPTER 24 STANDBY FUNCTION24.1 Standby Function and Configuration24.1.1 Standby functionThe standby function is designed to decrease power consumption of the system. The following two modes areavailable.(1) HALT modeHALT instruction execution sets the HALT mode. The HALT mode is intended to stop the CPU operationclock. System clock oscillator continues oscillation. In this mode, current consumption cannot be decreasedas in the STOP mode. The HALT mode is valid to restart immediately upon interrupt request and to carryout intermittent operations such as watch applications.(2) STOP modeSTOP instruction execution sets the STOP mode. In the STOP mode, the main system clock oscillator stopsand the whole system stops. CPU current consumption can be considerably decreased.Data memory low-voltage hold (down to V DD = 1.8 V) is possible. Thus, the STOP mode is effective to holddata memory contents with ultra-low current consumption. Because this mode can be cleared upon interruptrequest, it enables intermittent operations to be carried out.However, because a wait time is necessary to secure an oscillation stabilization time after the STOP modeis 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. 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 eitherthe main system clock or the subsystem clock.2. When proceeding to the STOP mode, be sure to stop the peripheral hardware operation andexecute the STOP instruction.3. The following sequence is recommended for power consumption reduction of the A/Dconverter when the standby function is used: first clear bit 7 (CS) to 0 to stop the A/Dconversion operation, and then execute the HALT or STOP instruction.
