Be sure to connect Vcc-RTC and Vss-RTC to a power supply even when not using RTC. Do not connect anything to XTAL2.
SH7709S, SH7729R, SH7706, SH7727: Please pull up EXTAL2 to Vcc (Internal Power supply).
SH7705: Please pull up EXTAL2 to VccQ (I/O power supply).
SH7720: Please pull up EXTAL_RTC to VccQ_RTC.
For details, please refer to the hardware manual "Appendix A Treatment of Unused Pins".