SH7708 datasheet(296/633 Pages) RENESAS

296 / 633 page

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Refreshing: The bus state controller includes a function for controlling pseudo-SRAM refreshing.

Distributed refreshing by means of auto-refresh cycles can be performed by clearing the RMODE

bit to 0 and setting the RFSH bit to 1 in MCR.

Refreshing is performed at intervals determined by the input clock selected by bits CKS2–CKS0

in RTCSR, and the value set in RTCOR. The value of bits CKS2–CKS0 in RTCOR should be set

so as to satisfy the refresh interval stipulation for the pseudo-SRAM used. First set the RTCOR,

RTCNT, and the RMODE and RFSH bits in MCR, then set the CKS2–CKS0. When the clock is

selected by CKS2–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. At the same time, RTCNT is cleared to zero

and the count-up is restarted. Figure 10.37 shows the auto-refresh cycle timing.

The number of

OE assert cycles for auto-refreshing is specified by the TRAS bits in MCR. The

precharge time from

OE negation until the next assertion of CE is determined by the setting of the

TPC bits in MCR.

Auto-refreshing is performed in normal operation, in sleep mode, and in a manual reset.

CKIO

TRc

OE/RFSH

TRr1

TRr2

(Tpc)

Figure 10.37 Pseudo-SRAM Auto-Refreshing

SH7708 Datasheet(PDF) 296 Page - Renesas Technology Corp