UPD78F1502AGK-GAK-AX Datasheet, PDF (239/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 5 CLOCK GENERATOR
Caution 1. When using the X1 oscillator and XT1 oscillator, wire as follows in the area enclosed by the
broken lines in the Figures 5-10 and 5-11 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 VSS. Do not
ground the capacitor to a ground pattern through which a high current flows.
• Do not fetch signals from the oscillator.
Note that the XT1 oscillator is designed as a low-gain circuit for achieving low-power consumption.
Note the following points when designing the XT1 oscillator.
• The pins and circuit board include parasitic capacitance. Therefore, confirm that there are no
problems by performing oscillation evaluation on the circuit board to be actually used.
• When low-consumption oscillation or super-low-consumption oscillation is selected, lower
power consumption than when selecting normal oscillation can be achieved. However, in this
case, the XT1 oscillation margin is reduced, so perform sufficient oscillation evaluation of the
resonator to be used for XT1 oscillation before using the resonator.
• Keep the wiring length between the XT1 and XT2 pins and resonator as short as possible and
parasitic capacitance and wire resistance as small as possible. This is particularly important
when super-low-consumption oscillation (AMPHS1 = 1) is selected.
• Configure the circuit board by using material with little parasitic capacitance and wire
resistance.
• Place a ground pattern that has the same potential as VSS (if possible) around the XT1 oscillator.
• Do not cross the signal lines between the XT1 and XT2 pins and the resonator with other signal
lines. Do not route the signal lines near a signal line through which a high fluctuating current
flows.
• Moisture absorption by the circuit board and condensation on the board in a highly humid
environment may cause the impedance between the XT1 and XT2 pins to drop and disable
oscillation. When using the circuit board in such an environment, prevent the circuit board
from absorbing moisture by taking measures such as coating the circuit board.
• Coat the surface of the circuit board by using material that does not generate capacitance or
leakage between the XT1 and XT2 pins.
Figure 5-12 shows examples of incorrect resonator connection.
R01UH0004EJ0501 Rev.5.01
223
Jun 20, 2011