Chapter 17 Standby Function; Standby Function And Configuration; Standby Function - NEC 78K0 User Manual

17.1 Standby Function and Configuration

17.1.1 Standby function

Table 17-1. Relationship Between Operation Clocks in Each Operation Status
Status X1 Oscillator
MSTOP = 0
Operation
MCC = 0
Mode
Reset Stopped
STOP
HALT Oscillating
Notes 1. When "Cannot be stopped" is selected for Ring-OSC by a mask option.
2. When "Can be stopped by software" is selected for Ring-OSC by a mask option.
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 a mask
option.
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
X1 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.
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CHAPTER 17 STANDBY FUNCTION

Ring-OSC Oscillator
MSTOP = 1 Note 1
MCC = 1
RSTOP = 0 RSTOP = 1
Stopped
Oscillating Oscillating
Stopped
User's Manual U16227EJ2V0UD
Subsystem
Clock
Oscillator
Note 2
Oscillating
Stopped
CPU Clock Prescaler Clock
After Supplied to Peripherals
Release
MCM0 = 0 MCM0 = 1
Ring-OSC Stopped
Note 3 Stopped
Note 4 Ring-OSC X1