153
the external bus is released
the RCDM bit or BE bit is cleared to 0
If a transition is made to the all-module-clocks-stopped mode in the
RAS
down state, the clock
will stop with
RAS
low. To enter the all-module-clocks-stopped mode with
RAS
high, the
RCDM bit must be cleared to 0 before executing the SLEEP instruction.
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 4.31 Example of Operation Timing in RAS Down Mode
(RAST = 0, CAST = 0)
•
RAS Up Mode
To select RAS up mode, clear the RCDM bit to 0 in DRAMCR. Each time access to DRAM
space is interrupted and another space is accessed, the
RAS
signal goes high again. Burst
operation is only performed if DRAM space is continuous. Figure 4.32 shows an example of
the timing in RAS up mode.
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