Renesas RL78 Series User Manual page 153

RL78/G1D
(a) Crystal oscillation
Caution When using the X1 oscillator and XT1 oscillator, wire as follows in the area enclosed by the
broken lines in the Figures 6-11 and 6-12 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
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.
● Before using the ultra-low power consumption oscillation (AMPHS1, AMPHS0 = 1, 0) as the
mode of the XT1 oscillator, evaluate the resonators described in 6.7 Resonator and Oscillator
Constants.
● 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
oscillator.
● Be sure that the signal lines between the XT1 and XT2 pins, and the resonators do not cross with
the other signal lines.
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.
R01UH0515EJ0120 Rev.1.20
Dec 16, 2016
Figure 6-12. Example of External Circuit of XT1 Oscillator
V
SS
XT1
32.768
kHz
XT2
Do not route the wiring near a signal line through which a high
CHAPTER 6 CLOCK GENERATOR
(b) External clock
External clock
as much as possible near the XT1
SS
EXCLKS
. Do not
SS
132