154
Normal space
read
DRAM space
read
T
p
T
r
T
c1
T
c2
T
1
T
2
DRAM space read
T
c1
T
c2
Note: n = 2 to 5
ø
RASn
(
CSn
)
UCAS
,
LCAS
RD
OE
Data bus
Address bus
Row address
Column address 1
Column address 2
External address
Figure 4.32 Example of Operation Timing in RAS Up Mode
(RAST = 0, CAST = 0)
4.5.13
Refresh Control
The H8S/2678 Series 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 the DRAMCR register.
CAS-before-RAS (CBR) Refreshing: To select CBR refreshing, set the RFSHE bit to 1 in
DRAMCR.
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.
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