AS4C1M16S-C&I
T0
T1
T2
T3
T4
T5
T6
T7
T8
CLK
READ A
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
COMMAND
CAS# Latency=2
tCK2, DQ
DOUT A0
DOUT A1
DOUT A0
DOUT A2
DOUT A1
DOUT A3
DOUT A2
CAS# Latency=3
tCK3, DQ
DOUT A3
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 LDQM/UDQM inputs two clocks
earlier (i.e. LDQM/UDQM 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).
T0
T1
T2
T3
T4
T5
T6
T7
T8
CLK
READ A
READ B
NOP
NOP
NOP
NOP
NOP
NOP
NOP
COMMAND
CAS# Latency=2
tCK2, DQ
DOUT A0
DOUT B0
DOUT A0
DOUT B1
DOUT B0
DOUT B2
DOUT B1
DOUT B3
DOUT B2
CAS# Latency=3
tCK3, DQ
DOUT B3
Figure 5. Read Interrupted by a Read
(Burst Length = 4, CAS# Latency = 2, 3)
The LDQM/UDQM inputs are used to avoid I/O contention on the DQ pins when the interrupt
comes from a Write command. The LDQM/UDQM 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 LDQM/UDQM must be asserted (HIGH) at least one
clock prior to the Write command to avoid internal bus contention.
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
CLK
DQM
Bank A
Activate
NOP
NOP
NOP
NOP
READ A
WRITE A
DIN A0
NOP
NOP
NOP
COMMAND
CAS# Latency=2
tCK2, DQ
DIN A1
DIN A2
DIN A3
Figure 6. Read to Write Interval
(Burst Length 4, CAS# Latency = 2)
Confidential
8
Rev. 2.0
March /2015
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
