System Clock Oscillator; Main System Clock Oscillator; External Circuit Of Main System Clock Oscillator - NEC mPD780208 Subseries User Manual

5.4 System Clock Oscillator

5.4.1 Main system clock oscillator

The main system clock oscillator oscillates with a crystal resonator or a ceramic resonator (standard: 5.0 MHz)
connected to the X1 and X2 pins.
External clocks can be input to the main system clock oscillator. In this case, input a clock signal to the X1 pin
and its inverted signal to the X2 pin.
Figure 5-6 shows an external circuit of the main system clock oscillator.
Figure 5-6. External Circuit of Main System Clock Oscillator
(a) Crystal or ceramic oscillation
Crystal or
ceramic resonator
Caution Do not execute the STOP instruction or set bit 7 (MCC) of the processor clock control register
(PCC) to 1 while an external clock is being input. This is because the operation of the main
system clock is stopped and the X2 pin is pulled up to V
or MCC is set to 1.
CHAPTER 5 CLOCK GENERATOR
External
IC
X1
clock
X2
User's Manual U11302EJ4V0UM
(b) External clock
X1
X2
if the STOP instruction is executed
DD
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