RX610 Group
8. Low Power Consumption
R01UH0032EJ0120 Rev.1.20
Page 192 of 1006
Feb 20, 2013
8.5.3
Software Standby Mode
8.5.3.1
Transition to Software Standby Mode
When the WAIT instruction is executed with the SSBY bit in SBYCR set to 1 and the DPSBY bit in DPSBYCR cleared
to 0, a transition to software standby mode is made. In this mode, the CPU, on-chip peripheral functions, and all the
oscillator functions stop. However, the contents of the CPU internal registers, on-chip RAM data, on-chip peripheral
functions, and the states of the I/O ports are retained. Whether the address bus and bus control signals are placed in the
high-impedance state or the output state is retained can be specified by the OPE bit in SBYCR. This mode allows
significant reduction in power consumption because the oscillator stops in this mode.
When a transition to software standby mode is made, the system clock (ICLK) and peripheral module clock (PCLK)
should be operating at the same frequency. If not, be sure to change the system clock (ICLK) or peripheral module clock
(PCLK) setting, before executing a WAIT instruction.
In addition, before executing a WAIT instruction, be sure to clear both the DMST bit in DMSCNT of the DMAC and the
DTCST bit in DTCST in the DTC to 0.
When the WDT is used in watchdog timer mode, no transition to software standby mode is made. Stop the WDT before
executing the WAIT instruction.
When software standby mode is in use, issue a WAIT instruction after making the following settings.
1. Clear the I bit
*
1
in PSW of the CPU to 0.
2. Set the priority
*
2
of the interrupt to be used for recovery from software standby mode to a level higher than the
setting of the IPL[2:0] bits
*
1
in PSW.
3. Set the IENj bit
*
2
in IERm for the interrupt to be used for recovery from software standby mode to 1.
4. Make either of the following settings for interrupts that are not to be used for recovery from software standby mode.
•
Set the priority*
2
of interrupts*
3
that are not to be used for recovery from software standby mode to a level lower
than the setting of the IPL[2:0] bits*
1
in PSW of the CPU.
•
Set the IENj bit*
2
in IERm for the interrupt*
3
that is not to be used for recovery from software standby mode to
0.
5. Execute a WAIT instruction (executing a WAIT instruction causes automatic setting of the I bit
*
1
in PSW of the
CPU to 1).
Notes: 1. For details, see section 2, CPU.
2.
For details, see section 10, Interrupt Control Unit (ICU).
3.
Executing a WAIT instruction while a peripheral module is operating creates a possibility of recovery from
software standby mode being triggered by an interrupt that could not normally act as a trigger for recovery.
In addition, the interrupt status flag of an interrupt IRQ0 to IRQ15, which is not specified as a trigger for
recovery, might be set in software standby mode, and thus an unexpected exception handling that is not the
trigger for recovery will be started.
Interrupts that can act as triggers for recovery thus includes all interrupts which can be set by the various
IERi.IENj bits and the PSW.IPL[2:0] bits, as well as the interrupts that are intended to act as triggers for
recovery.
Summary of Contents for RX600 Series
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