NEC PD78052 - External Circuit of Main System Clock Oscillator; System Clock Oscillator; Main System Clock Oscillator

165
CHAPTER 7 CLOCK GENERATOR
Crystal
or
Ceramic Resonator
IC
X1
X2
X1
PD74HCU04
µ
X2
External
Clock
7.4 System Clock Oscillator
7.4.1 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 an antiphase clock signal to the X2 pin.
Figure 7-6 shows an external circuit of the main system clock oscillator.
Figure 7-6. External Circuit of Main System Clock Oscillator
(a) Crystal and ceramic oscillation (b) External clock
Caution Do not execute the STOP instruction or do not set MCC (bit 7 of processor clock control register
(PCC)) to 1 if an external clock is used. This is because if STOP instruction is executed or MCC
is set to 1, the operation of the main system clock is stopped and the X2 pin is pulled up to V
DD.