Datasheet

Section 6 Bus Controller (BSC)
R01UH0310EJ0500 Rev. 5.00 Page 241 of 1384
Sep 25, 2012
H8S/2426, H8S/2426R, H8S/2424 Group
6.7.12 Refresh Control
This LSI is provided with a DRAM refresh control function. CAS-before-RAS (CBR) refreshing
is used. In addition, self-refreshing can be executed when the chip enters the software standby
state.
Refresh control is enabled when any area is designated as DRAM space in accordance with the
setting of bits RMTS2 to RMTS0 in DRAMCR.
(1) CAS-before-RAS (CBR) Refreshing
To select CBR refreshing, set the RFSHE bit to 1 in REFCR.
With CBR refreshing, RTCNT counts up using the input clock selected by bits RTCK2 to RTCK0
in REFCR, and when the count matches the value set in RTCOR (compare match), refresh control
is performed. 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 RTCK2 to RTCK0.
Set a value in RTCOR and bits RTCK2 to RTCK0 that will meet the refreshing interval
specification for the DRAM used.
When bits RTCK2 to RTCK0 in REFCR are set, RTCNT starts counting up. RTCNT and RTCOR
settings should therefore be completed before setting bits RTCK2 to RTCK0. RTCNT operation is
shown in figure 6.46, compare match timing in figure 6.47, and CBR refresh timing in figure 6.48.
When the CBRM bit in REFCR is cleared to 0, access to external space other than DRAM space is
performed in parallel during the CBR refresh period.
RTCOR
H'00
Refresh request
RTCNT
Figure 6.46 RTCNT Operation