SH7720 Datasheet, PDF (437/1524 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 9 Bus State Controller (BSC)
CKIO
A25 to A0
A12/A11*¹
CSn
RAS
CAS
RD/WR
DQMxx
D31 to D0
BS
DACKn*²
Tp
Tpw
Trr
Trc
Trc
Trc
Hi-z
Notes: 1. Address pin to be connected to the A10 pin of SDRAM.
2. The waveform for DACKn is when active low is specified.
Figure 9.25 Auto-Refresh Timing
(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 9.26. 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
Rev. 3.00 Jan. 18, 2008 Page 375 of 1458
REJ09B0033-0300