SH7730 Datasheet, PDF (594/1188 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7780 Series

Section 17 Realtime Clock (RTC)
17.5.3 Transition to Standby Mode after Setting Register
When a transition to standby mode is made after registers in the RTC are set, sometimes counting
is not performed correctly. In case the registers are set, be sure to make a transition to standby
mode after waiting for two RTC clocks or more.
17.5.4 Crystal Oscillator Circuit
An example of the RTC crystal oscillator circuit is shown in figure 17.6.
This LSI
R_f
EXTAL_RTC
R_D
XTAL_RTC
XTAL
C_in
C_out
Notes: 1. Select either the Cin or Cout side for frequency adjustment variable capacitor
according to requirements such as frequency range, degree of stability, etc.
2. Built-in resistance value Rf (Typ value) = 10 MΩ, RD (Typ value) = 400 kΩ
3. Cin and Cout values include floating capacitance due to the wiring. Take care
when using a ground plane.
4. The crystal oscillation settling time depends on the mounted circuit constants,
stray capacitance, etc., and should be decided after consultation with the
crystal resonator manufacturer.
5. Place the crystal resonator and load capacitors Cin and Cout as close as
possible to the chip.
(Correct oscillation may not be possible if there is externally induced noise in
the EXTAL_RTC and XTAL_RTC pins.)
6. Ensure that the crystal resonator connection pin (EXTAL_RTC, XTAL_RTC)
wiring is routed as far away as possible from other power lines (except GND)
and signal lines.
Figure 17.6 Example of Crystal Oscillator Circuit Connection
Rev. 1.00 Sep. 19, 2007 Page 546 of 1136
REJ09B0359-0100