SH7263 Datasheet, PDF (373/1862 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7260 Series

Section 9 Bus State Controller (BSC)
(8) Refreshing
This LSI has a function for controlling SDRAM refreshing. Auto-refreshing can be performed by
clearing the RMODE bit to 0 and setting the RFSH bit to 1 in SDCR. A continuous refreshing can
be performed by setting the RRC2 to RRC0 bits in RTCSR. If SDRAM is not accessed for a long
period, self-refresh mode, in which the power consumption for data retention is low, can be
activated by setting both the RMODE bit and the RFSH bit to 1.
(a) Auto-refreshing
Refreshing is performed at intervals determined by the input clock selected by bits CKS2 to CKS0
in RTCSR, and the value set by in RTCOR. The value of bits CKS2 to CKS0 in RTCOR should
be set so as to satisfy the refresh interval stipulation for the SDRAM used. First make the settings
for RTCOR, RTCNT, and the RMODE and RFSH bits in SDCR, then make the CKS2 to CKS0
and RRC2 to RRC0 settings. When the clock is selected by bits CKS2 to CKS0, RTCNT starts
counting up from the value at that time. The RTCNT value is constantly compared with the
RTCOR value, and if the two values are the same, a refresh request is generated and an auto-
refresh is performed for the number of times specified by the RRC2 to RRC0. At the same time,
RTCNT is cleared to zero and the count-up is restarted.
Figure 9.28 shows the auto-refresh cycle timing. After starting, the auto refreshing, PALL
command is issued in the Tp cycle to make all the banks to pre-charged state from active state
when some bank is being pre-charged. Then REF command is issued in the Trr cycle after
inserting idle cycles of which number is specified by the WTRP1 and WTRP0 bits in CS3WCR. A
new command is not issued for the duration of the number of cycles specified by the WTRC1 and
WTRC0 bits in CS3WCR after the Trr cycle. The WTRC1 and WTRC0 bits must be set so as to
satisfy the SDRAM refreshing cycle time stipulation (tRC). An idle cycle is inserted between the
Tp cycle and Trr cycle when the setting value of the WTRP1 and WTRP0 bits in CS3WCR is
longer than or equal to 1 cycle.
Rev. 2.00 Mar. 14, 2008 Page 339 of 1824
REJ09B0290-0200