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Auto-refresh command[REF]:
When this
command is input from the IDLE state, the
synchronous
DRAM
starts
auto-refresh
operation. (The auto-refresh is the same as the
CBR refresh of conventional DRAMs.) During
the auto-refresh operation, refresh address and
bank select address are generated inside the
synchronous DRAM. For every auto-refresh
cycle, the internal address counter is updated.
Accordingly, 4,096 times are required to refresh
the entire memory. Before executing the auto-
refresh command, all the banks must be in the
IDLE state. In addition, since the Precharge for
all banks is automatically performed after auto-
refresh, no Precharge command is required after
auto-refresh.
Self-refresh entry[SELF]:
When this command
is input during the IDLE state, the synchronous
DRAM starts self-refresh operation. After the
execution of this command, self-refresh
continues while CKE is Low. Since self-refresh
is performed internally and automatically,
external refresh operations are unnecessary.
GM72V66841CT/CLT
Self-refresh exit[SELFX]:
When this command
is executed during self-refresh mode, the
synchronous DRAM can exit from self-refresh
mode. After exiting from self-refresh mode, the
synchronous DRAM enters the IDLE state.
Power down mode entry:
When this command
is executed during the IDLE state, the
synchronous DRAM enters Power down mode.
In Power down mode, Power consumption is
suppressed by cutting off the initial input circuit.
Power down exit:
When this command is
executed at the Power down mode, the
synchronous DRAM can exit from Power down
mode. After exiting from Power down mode, the
synchronous DRAM enters the IDLE state.
Function Truth Table
The following table shows the operations that are performed when each command is issued in each
mode of the synchronous DRAM.
Current
state
Precharge
CS
H
L
L
L
L
L
L
RAS
X
H
H
H
H
L
L
CAS
X
H
H
L
L
H
H
WE
X
H
L
H
L
H
L
X
X
X
Address
Command
DESL
NOP
BST
Operation
Enter IDLE after
Enter IDLE after
NOP
t
RP
t
RP
BA, CA, A10 READ/READ A ILLEGAL
BA, CA, A10 WRIT/WRIT A
BA, RA
BA, A10
ACTV
PRE, PALL
ILLEGAL
ILLEGAL
NOP
8
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