EM638165
EtronTech
T0
T1
T2
T3
T4
T5
T6
T7
T8
CLK
READ A
NOP
NOP
NOP
NOP
NOP
NOP
NOP
NOP
COMMAND
CAS# Latency=2
DOUT A0
DOUT A1
DOUT A0
DOUT A2
DOUT A1
DOUT A3
DOUT A2
t
CK2, DQ
CAS# Latency=3
tCK3, DQ
DOUT A3
Figure 5. 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).
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
DOUT A0
DOUT B0
DOUT A0
DOUT B1
DOUT B0
DOUT B2
DOUT B1
DOUT B3
DOUT B2
t
CK2, DQ
CAS# Latency=3
tCK3, DQ
DOUT B3
Figure 6. 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.
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 7. Read to Write Interval
(Burst Length ≥ 4, CAS# Latency = 2)
Rev. 5.2
8
Rev. 5.2
Dec. /2013
ETRON [ ETRON TECHNOLOGY, INC. ]
