Datasheet
Table Of Contents
CLK
COMMAND
T0
T1 T2 T3 T4 T5 T6
READ A NOP NOP NOP NOP NOP NOP NOP
T7 T8
NOP
CAS# Latency=2
t
CK2
, DQ
CAS# Latency=3
t
CK3
, DQ
DOUT A
0
DOUT A
1
DOUT A
2
DOUT A
3
DOUT A
0
DOUT A
1
DOUT A
2
DOUT A
3
Figure 4. Burst Read Operation
(Burst Length = 4, CAS# Latency = 2, 3)
The read data appears on the DQs subject to the values on the DQM inputs two clocks earlier (i.e. DQM
latency is two clocks for output buffers). A read burst without the auto precharge function may be
interrupted by a subsequent Read or Write command to the same bank or the other active bank before
the end of the burst length. It may be interrupted by a BankPrecharge/ PrechargeAll command to the
same bank too. The interrupt coming from the Read command can occur on any clock cycle following a
previous Read command (refer to the following figure).
CLK
COMMAND
T0
T1 T2 T3 T4 T5 T6
READ A READ B NOP NOP NOP NOP NOP NOP
T7 T8
NOP
CAS# Latency=2
t
CK2
, DQ
CAS# Latency=3
t
CK3
, DQ
DOUT A
0
DOUT B
0
DOUT B
1
DOUT B
2
DOUT A
0
DOUT B
0
DOUT B
1
DOUT B
2
DOUT B
3
DOUT B
3
Figure 5. Read Interrupted by a Read
(Burst Length = 4, CAS# Latency = 2, 3)
The DQM inputs are used to avoid I/O contention on the DQ pins when the interrupt comes from a Write
command. The DQMs must be asserted (HIGH) at least two clocks prior to the Write command to
suppress data-out on the DQ pins. To guarantee the DQ pins against I/O contention, a single cycle with
high-impedance on the DQ pins must occur between the last read data and the Write command (refer to
the following three figures). If the data output of the burst read occurs at the second clock of the burst
write, the DQMs must be asserted (HIGH) at least one clock prior to the Write command to avoid internal
bus contention.
CLK
COMMAND
T0
T1 T2 T3 T4 T5 T6
NOP NOP
Bank A
Activate
NOP NOP READ A WRITE A NOP
T7 T8
NOP
CAS# Latency=2
t
CK2
, DQ
DQM
T9
NOP
DIN A
0
DIN A
1
DIN A
2
DIN A
3
Figure 6. Read to Write Interval
(Burst Length 4, CAS# Latency = 2)
AS4C4M16SA-C&I
Confidential
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Rev.5.0 October 2018