RL78/G15 CHAPTER 15 STANDBY FUNCTION
R01UH0959EJ0110 Rev.1.10 Page 624 of 765
Mar 7, 2023
CHAPTER 15 STANDBY FUNCTION
15.1 Overview
The standby function reduces the operating current of the system, and 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 or high-speed on-chip 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 high-
speed on-chip 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 status are also held.
Caution 1. When shifting to the STOP mode, be sure to stop the peripheral hardware operation operating with
X1 oscillation or EXCLK input before executing STOP instruction
Note 1
.
Caution 2. 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 A/D converter mode
register 0 (ADM0) to 0 to stop the A/D conversion operation, and then execute the STOP
instruction.
Caution 3. It can be selected by the option byte whether the low-speed on-chip oscillator continues oscillating
or stops in the HALT or STOP mode. For details, see CHAPTER 18 OPTION BYTE.
Note 1. 16-pin and 20-pin products only.
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