R01UH0823EJ0100 Rev.1.00
Page 239 of 1823
Jul 31, 2019
RX23W Group
11. Low Power Consumption
11.3
Reducing Power Consumption by Switching Clock Signals
The clock frequency can change by setting the SCKCR.FCK[3:0], ICK[3:0], PCKA[3:0], PCKB[3:0], and PCKD[3:0]
bits. The CPU, DMAC, DTC, ROM, and RAM clocks can be set by the ICK[3:0] bits. The peripheral module clocks can
be set by the PCKA[3:0], PCKB[3:0], and PCKD[3:0] bits.
The flash memory clock can be set by the FCK[3:0] bits.
For details, refer to
section 9, Clock Generation Circuit
.
11.4
Module Stop Function
The module stop function can be set for each on-chip peripheral module.
When the MSTPmi bit (m = A to D; i = 0 to 31) in MSTPCRA to MSTPCRD is set to 1, the specified module stops
operating and enters the module stop state, but the CPU continues to operate independently. When the corresponding
MSTPmi bit is set to 0, the module exits the module state and restarts operating at the end of the bus cycle. The internal
states of modules are retained in the module stop state.
After a reset is canceled, all modules other than the DMAC, DTC, and on-chip RAM are in the module stop state.
Basically the registers in the module stop state cannot be read or written. However, note that data may be written to these
registers if write access is made immediately after the setting of the module stop state. To avoid this, always write to the
module stop registers after confirming that the last register setting is done.
11.5
Function for Lower Operating Power Consumption
By selecting an appropriate operating power control mode according to the operating frequency and operating voltage,
power consumption can be reduced in normal mode, sleep mode, and deep sleep mode.
11.5.1
Setting Operating Power Control Mode
Examples of the procedures for switching operating power control modes are shown below:
(1) Switching from Normal Power Consumption Mode to Low Power Consumption Mode
Example 1: From high-speed operating mode to middle-speed operating mode
(High-speed operation in high-speed operating mode)
↓
Set the frequency of each clock to lower than the maximum operating frequency for middle-speed operating mode
↓
Confirm that the OPCCR.OPCMTSF flag is 0 (transition completed)
↓
Set the OPCCR.OPCM[2:0] bits to 010b (middle-speed operating mode)
↓
Confirm that the OPCCR.OPCMTSF flag is 0 (transition completed)
↓
(Middle-speed operation in middle-speed operating mode)