MT48LC4M8A1TG-10 View Datasheet(PDF) - Micron Technology
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MT48LC4M8A1TG-10 Datasheet PDF : 50 Pages
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CAS Latency
The CAS latency is the delay, in clock cycles, between
the registration of a READ command and the availability
of the first piece of output data. The latency can be set to
1, 2, or 3 clocks.
If a READ command is registered at clock edge n, and
the latency is m clocks, the data will be available by clock
edge n + m. The DQs will start driving as a result of the
clock edge one cycle earlier (n + m - 1) and, provided that
the relevant access times are met, the data will be valid by
clock edge n + m. For example, assuming that the clock
cycle time is such that all relevant access times are met,
if a READ command is registered at T0, and the latency is
programmed to two clocks, the DQs will start driving
after T1 and the data will be valid by T2, as shown in
Figure 2. Table 2 below indicates the operating frequen-
cies at which each CAS latency setting can be used.
CLK
COMMAND
DQ
Figure 2
CAS LATENCY
T0
T1
T2
READ
tLZ
tAC
NOP
tOH
DOUT
CAS Latency = 1
T0
T1
T2
T3
CLK
COMMAND
DQ
READ
NOP
tLZ
tAC
CAS Latency = 2
NOP
tOH
DOUT
16 MEG: x4, x8
SDRAM
Reserved states should not be used, as unknown op-
eration or incompatibility with future versions may re-
sult.
Operating Mode
The normal operating mode is selected by setting M7
and M8 to zero; the other combinations of values for M7
and M8 are reserved for future use and/or test modes.
The programmed burst length applies to both READ and
WRITE bursts.
Test modes and reserved states should not be used
because unknown operation or incompatibility with fu-
ture versions may result.
Write Burst Mode
When M9 = 0, the burst length programmed via M0-
M2 applies to both READ and WRITE bursts; when
M9 = 1, the programmed burst length applies to READ
bursts, but write accesses are single-location (nonburst)
accesses.
Table 2
CAS LATENCY
SPEED
-8D/E
-8A/B/C
-10
ALLOWABLE OPERATING
FREQUENCY (MHz)
CAS
CAS
CAS
LATENCY = 1 LATENCY = 2 LATENCY = 3
£ 33
£ 100
£ 125
£ 33
£ 83
£ 125
£ 33
£ 66
£ 100
CLK
COMMAND
T0
READ
DQ
T1
T2
NOP
NOP
tLZ
tAC
CAS Latency = 3
16 Meg: x4, x8 SDRAM
16MSDRAMx4x8_B.p65 – Rev. 5/98
T3
T4
NOP
tOH
DOUT
DON’T CARE
UNDEFINED
9
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©1998, Micron Technology, Inc.
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