SH7730 Datasheet, PDF (423/1188 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7780 Series

Section 11 Bus State Controller (BSC)
(b) Self-refreshing
Self-refresh mode in which the refresh timing and refresh addresses are generated within the
SDRAM. Self-refreshing is activated by setting both the RMODE bit and the RFSH bit in
SDCR to 1. After starting the self-refreshing, PALL command is issued in Tp cycle after the
completion of the pre-charging bank. A SELF command is then issued after inserting idle
cycles of which number is specified by the TRP[1:0] bits in CSnWSR. SDRAM cannot be
accessed while in the self-refresh state. Self-refresh mode is cleared by clearing the RMODE
bit to 0. After self-refresh mode has been cleared, command issuance is disabled for the
number of cycles specified by the TRC[1:0] bits in CSnWCR.
Self-refresh timing is shown in figure 11.26. Settings must be made so that self-refresh
clearing and data retention are performed correctly, and auto-refreshing is performed at the
correct intervals. When self-refreshing is activated from the state in which auto-refreshing is
set, or when exiting standby mode other than through a power-on reset, auto-refreshing is
restarted if the RFSH bit is set to 1 and the RMODE bit is cleared to 0 when self-refresh mode
is cleared. If the transition from clearing of self-refresh mode to the start of auto-refreshing
takes time, this time should be taken into consideration when setting the initial value of
RTCNT. Making the RTCNT value 1 less than the RTCOR value will enable refreshing to be
started immediately.
After self-refreshing has been set, the self-refresh state continues even if the chip standby state
is entered using the LSI standby function, and is maintained even after recovery from standby
mode by an interrupt.
The self-refresh state is not cleared by a manual reset.
In case of a power-on reset, the bus state controller’s registers are initialized, and therefore the
self-refresh state is cleared.
Rev. 1.00 Sep. 19, 2007 Page 375 of 1136
REJ09B0359-0100