SH7751 Datasheet, PDF (351/1224 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

9. Power-Down Modes
The module standby function is not exited by means of a power-on reset via the RESET pin or a
power-on reset caused by watchdog timer overflow.
9.8 Hardware Standby Mode
9.8.1 Transition to Hardware Standby Mode
Setting the CA pin level low effects a transition to hardware standby mode. In this mode, all
modules other than the RTC stop, as in the standby mode selected using the SLEEP command.
Hardware standby mode differs from standby mode as follows:
1. Interrupts and manual resets are not available;
2. All output pins other than the STATUS pin are in the high-impedance state and the pull-up
resistance is off.
3. On the SH7751, the RTC continues to operate even when no power is supplied to power pins
other than the RTC power supply pin.
The status of the STATUS pin is determined by the STHZ bit of STBCR2. See section D, Pin
Functions, for details of output pin states.
Operation when a low-level is input to the CA pin when in the standby mode depends on the CPG
status, as follows:
1. In standby mode
The clock remains stopped and a transition is made to the hardware standby state.
Interrupts and manual resets are disabled, but the output pins remain in the same state as in
standby mode.
2. When WDT is operating when standby mode is exited by interrupt
Standby mode is momentarily exited, the CPU restarts, and then a transition is made to
hardware standby mode.
Note that the level of the CA pin must be kept low while in hardware standby mode.
9.8.2 Exit from Hardware Standby Mode
Hardware standby mode can only be cancelled by a power-on reset. Driving the CA pin high when
the RESET pin is being driven low causes clock oscillation to start. At this point, maintain the
RESET pin at low level until clock oscillation stabilizes. The CPU will start power-on reset
processing if the RESET pin is driven high. Hardware standby mode cannot be cancelled by an
interrupt or a manual reset.
Rev.4.00 Oct. 10, 2008 Page 253 of 1122
REJ09B0370-0400