SH7261 Datasheet, PDF (1178/1348 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7260 Series

Section 27 Power-Down Modes
27.3.4 Deep Standby Mode
(1) Transition to Deep Standby Mode
The LSI switches from a program execution state to deep standby mode by executing the SLEEP
instruction when the STBY bit and DEEP bit in STBCR are set to 1. In deep standby mode, not
only the CPU, clocks, and on-chip peripheral modules but also power supply is turned off
excluding the on-chip RAM retaining area specified by the RAMKP3 to RAMKP0 bits in the
RAMKP register and RTC. This can significantly reduce power consumption. Therefore, data in
the registers of the CPU, cache, and on-chip peripheral modules are not retained. Pin state values
immediately before the transition to deep standby mode can be retained.
The CPU takes one cycle to finish writing to DSFR, and then executes processing for the next
instruction. However, it actually takes one or more cycles to write. Therefore, execute a SLEEP
instruction after reading DSFR to have the values written to DSFR by the CPU to be definitely
reflected in the SLEEP instruction.
The procedure for switching to deep standby mode is as follows. Figure 27.2 also shows its
flowchart.
1. Set the RAMKP3 to RAMKP0 bits in the RAMKP register for the corresponding on-chip
RAM retaining area.
2. Execute read and write of an arbitrary but the same address for each page in the retaining
RAM area. When this is not executed, data last written may not be stored in the on-chip RAM.
If there is a write to the on-chip RAM after this time, execute this processing after the last
write to the on-chip RAM.
3. Set the CKS[2:0] bits in the DSCNT register so that the initial value of FRQCR in the CPG
becomes larger than the oscillation settling time.
4. Set the STBY and DEEP bits in the STBCR register to 1.
5. Read out the DSFR register after clearing the flag in the DSFR register. Then execute the
SLEEP instruction.
Rev. 2.00 Sep. 07, 2007 Page 1146 of 1312
REJ09B0320-0200