UPD780138 Datasheet, PDF (119/558 Pages) NEC – 8-Bit Single-Chip Microcontrollers

CHAPTER 5 CLOCK GENERATOR
5.3 Registers Controlling Clock Generator
The following six registers are used to control the clock generator.
• Processor clock control register (PCC)
• Ring-OSC mode register (RCM)
• Main clock mode register (MCM)
• Main OSC control register (MOC)
• Oscillation stabilization time counter status register (OSTC)
• Oscillation stabilization time select register (OSTS)
(1) Processor clock control register (PCC)
The PCC register is used to select the CPU clock, the division ratio, main system clock oscillator operation/stop
and whether to use the on-chip feedback resistor^Note of the subsystem clock oscillator.
The PCC is set by a 1-bit or 8-bit memory manipulation instruction.
RESET input clears PCC to 00H.
Note The feedback resistor is required to control the bias point of the oscillation waveform so that the bias point
is in the middle of the power supply voltage.
When the subsystem clock is not used, the operating current in the STOP mode can be reduced by setting
bit 6 (FRC) of PCC to 1 (see Figure 5-11 Subsystem Clock Feedback Resistor).
User’s Manual U16228EJ2V0UD
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