User’s Manual U16899EJ2V0UD
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CHAPTER 19 STANDBY FUNCTION
19.1 Standby Function and Configuration
19.1.1 Standby function
Table 19-1. Relationship Between Operation Clocks in Each Operation Status
High-Speed System
Clock Oscillator
Ring-OSC Oscillator
Prescaler Clock
Supplied to Peripherals
Note 2
Status
Operation
Mode
MSTOP = 0
MCC = 0
MSTOP = 1
MCC = 1
Note 1
RSTOP = 0 RSTOP = 1
Subsystem
Clock
Oscillator
CPU Clock
After
Release
MCM0 = 0 MCM0 = 1
Reset Stopped
Ring-OSC
Stopped
STOP
Stopped
Note 3
Stopped
HALT Oscillating
Stopped
Oscillating Oscillating Stopped
Oscillating
Note 4
Ring-OSC High-
speed
system
clock
Notes 1. When “Cannot be stopped” is selected for Ring-OSC by the option byte.
2. When “Can be stopped by software” is selected for Ring-OSC by the option byte.
3. Operates using the CPU clock at STOP instruction execution.
4. Operates using the CPU clock at HALT instruction execution.
Caution The RSTOP setting is valid only when “Can be stopped by software” is set for Ring-OSC by the
option byte.
Remark MSTOP: Bit 7 of the main OSC control register (MOC)
MCC:
Bit 7 of the processor clock control register (PCC)
RSTOP: Bit 0 of the Ring-OSC mode register (RCM)
MCM0:
Bit 0 of the main clock mode register (MCM)
The standby function is designed to reduce the operating current of the system. 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, Ring-OSC oscillator, or subsystem clock 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.