Renesas RL78 Series User Manual

RL78/F13, F14 CHAPTER 5 CLOCK GENERATOR
R01UH0368EJ0210 Rev.2.10 396
Dec 10, 2015
Figure 5-24. Example of External Circuit of XT1 Oscillator
(a) Crystal oscillation (b) External clock
Caution When using the X1 oscillator and XT1 oscillator, wire as follows in the area enclosed by the broken
lines in Figures 5-23 and 5-24 to avoid an adverse effect from wiring capacitance.
• Keep the wiring length as short as possible.
• Do not cross the wiring with the other signal lines. Do not route the wiring near a signal line
through which a high fluctuating current flows.
• Always make the ground point of the oscillator capacitor the same potential as V
SS. Do not ground
the capacitor to a ground pattern through which a high current flows.
• Do not fetch signals from the oscillator.
The XT1 oscillator is a circuit with low amplification in order to achieve low-power consumption. Note
the following points when designing the circuit.
 Pins and circuit boards include parasitic capacitance. Therefore, perform oscillation evaluation
using a circuit board to be actually used and confirm that there are no problems.
 Make the wiring between the XT1 and XT2 pins and the resonators as short as possible, and
minimize the parasitic capacitance and wiring resistance. Note this particularly when the ultra-
low power consumption oscillation (AMPHS1, AMPHS0 = 1, 0) is selected.
 Configure the circuit of the circuit board, using material with little wiring resistance.
 Place a ground pattern that has the same potential as V
SS as much as possible near the XT1
oscillator.
 Be sure that the signal lines between the XT1 and XT2 pins, and the resonators do not cross with
the other signal lines. Do not route the wiring near a signal line through which a high fluctuating
current flows.
 The impedance between the XT1 and XT2 pins may drop and oscillation may be disturbed due to
moisture absorption of the circuit board in a high-humidity environment or dew condensation on
the board. When using the circuit board in such an environment, take measures to damp-proof
the circuit board, such as by coating.
 When coating the circuit board, use material that does not cause capacitance or leakage between
the XT1 and XT2 pins.
XT2
XT1
32.768
kHz
V
SS
EXCLKS
External clock

Renesas RL78 Series Specifications

General

Brand	Renesas
Model	RL78 Series
Category	Computer Hardware
Language	English