Example Of Controlling Internal Low-Speed Oscillation Clock; Clocks Supplied To Cpu And Peripheral Hardware - NEC 78K0 Series User Manual

6.6.4 Example of controlling internal low-speed oscillation clock

The internal low-speed oscillation clock cannot be used as the CPU clock.
Only the following peripheral hardware can operate with this clock.
• Watchdog timer
• 8-bit timer H1 (if f
is selected as the count clock)
RL
In addition, the following operation modes can be selected by the option byte.
• Internal low-speed oscillator cannot be stopped
• Internal low-speed oscillator can be stopped by software
The internal low-speed oscillator automatically starts oscillation after a reset release, and the watchdog timer is
driven (240 kHz (TYP.)) if the watchdog timer operation has been enabled by the option byte.
(1) Example of setting procedure when stopping the internal low-speed oscillation clock
<1> Setting LSRSTOP to 1 (RCM register)
When LSRSTOP is set to 1, the internal low-speed oscillation clock is stopped.
(2) Example of setting procedure when restarting oscillation of the internal low-speed oscillation clock
<1> Clearing LSRSTOP to 0 (RCM register)
When LSRSTOP is cleared to 0, the internal low-speed oscillation clock is restarted.
Caution If "Internal low-speed oscillator cannot be stopped" is selected by the option byte, oscillation of
the internal low-speed oscillation clock cannot be controlled.

6.6.5 Clocks supplied to CPU and peripheral hardware

The following table shows the relation among the clocks supplied to the CPU and peripheral hardware, and setting
of registers.
Table 6-4. Clocks Supplied to CPU and Peripheral Hardware, and Register Setting
Clock Supplied to CPU
Internal high-speed oscillation clock
Internal high-speed oscillation clock
X1 clock
External main system clock
Subsystem clock
Remarks 1. XSEL: Bit 2 of the main clock mode register (MCM)
2. CSS: Bit 4 of the processor clock control register (PCC)
3. MCM0: Bit 0 of MCM
4. EXCLK: Bit 7 of the clock operation mode select register (OSCCTL)
5. ×:
don't care
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CHAPTER 6 CLOCK GENERATOR
Supplied Clock
Clock Supplied to Peripheral Hardware
X1 clock
External main system clock
Internal high-speed oscillation clock
X1 clock
External main system clock
Preliminary User's Manual U17260EJ3V1UD
XSEL CSS MCM0
×
0 0
1 0 0
1 0 0
1 0 1
1 0 1
×
0 1
1 1 0
1 1 1
1 1 0
1 1 1
EXCLK
×
0
1
0
1
×
0
0
1
1