H8SLASH3028F datasheet(193/923 Pages) RENESAS

193 / 923 page

Rev. 2.00, 09/03, page 163 of 890

6.5.11

Refresh Control

The H8/3028 Group is provided with a CAS-before-RAS (CBR) function and self-refresh function

as DRAM refresh control functions.

CAS-Before-RAS (CBR) Refreshing: To select CBR refreshing, set the RCYCE bit to 1 in

DRCRB.

With CBR refreshing, RTCNT counts up using the input clock selected by bits CKS2 to CKS0 in

RTMCSR, and a refresh request is generated when the count matches the value set in RTCOR

(compare match). At the same time, RTCNT is reset and starts counting up again from H'00.

Refreshing is thus repeated at fixed intervals determined by RTCOR and bits CKS2 to CKS0. A

refresh cycle is executed after this refresh request has been accepted and the DRAM interface has

acquired the bus. Set a value in bits CKS2 to CKS0 in RTCOR that will meet the refresh interval

specification for the DRAM used. When RAS down mode is used, set the refresh interval so that

the maximum

RAS pulse width specification is met.

RTCNT starts counting up when bits CKS2 to CKS0 are set. RTCNT and RTCOR settings should

therefore be completed before setting bits CKS2 to CKS0.

Also note that a repeat refresh request generated during a bus request, or a refresh request during

refresh cycle execution, will be ignored.

RTCNT operation is shown in figure 6.26, compare match timing in figure 6.27, and CBR refresh

timing in figures 6.28 and 6.29.

RTCNT

RTCOR

H'00

Refresh request

Figure 6.26 RTCNT Operation

H8/3028F 数据表(PDF) 193 Page - Renesas Technology Corp