SH7763 Datasheet, PDF (750/2026 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC Engine Family SH-4A Series

Section 18 Power-Down Mode
18.8 RTC Power Supply Backup
18.8.1 Transition to RTC Power Supply Backup Mode
When entering the RTC power supply backup mode with the VDD power supply (1.2 V) turned
off, the VDD power supply should be turned off while the XRTCSTBI signal is held low. By
turning off the VDD power supply, the currents that might be generated in the VDD (1.2 V)
operating region can be eliminated to reduce power consumption. If the clock has been supplied
from the 32.768-Hz crystal, the RTC continues counting of its second to year counters while the
VDD (1.2 V) power supply is turned off.
18.8.2 Canceling RTC Power Supply Backup Mode
The RTC power supply backup mode is canceled by a power-on reset. Even when any interrupt
condition is satisfied in the RTC power supply backup mode, the interrupt-generating condition
will be canceled by the power-on reset. RTC power supply backup mode can be canceled in the
following steps.
1. Turn on the VDD power supply (1.2 V) while holding the PRESET signal low.
2. Since the VDD-RTC (3.3 V), which is exclusively used for the RTC, is supplied, drive the
XRTCSTBI signal high only after the power-on oscillation stabilization time has elapsed after
the VDD (1.2 V) becomes stable. This is to prevent the LSI from being damaged by the
transient current.
3. Hold the PRESET signal low until the RTC is reset by the power-on reset, and then cancel the
power-on reset.
Table 18.5 shows the configuration of the pins related to RTC power supply backup mode.
Table 18.5 Pin Configuration
Pin Name
XRTCSTBI
Function
RTC standby
I/O
Input
Description
When this pin goes low, the LSI enters RTC
power supply backup mode.
Rev. 1.00 Oct. 01, 2007 Page 684 of 1956
REJ09B0256-0100