NT5DS64M4AT Datasheet, PDF (17/78 Pages) List of Unclassifed Manufacturers – 256Mb Double Data Rate SDRAM

NT5DS64M4AT NT5DS64M4AW
NT5DS32M8AT NT5DS32M8AW
256Mb Double Data Rate SDRAM
Auto Precharge
Auto Precharge is a feature which performs the same individual-bank precharge function described above, but without requiring
an explicit command. This is accomplished by using A10 to enable Auto Precharge in conjunction with a specific Read or Write
command. A precharge of the bank/row that is addressed with the Read or Write command is automatically performed upon
completion of the Read or Write burst. Auto Precharge is nonpersistent in that it is either enabled or disabled for each individual
Read or Write command. Auto Precharge ensures that the precharge is initiated at the earliest valid stage within a burst. This is
determined as if an explicit Precharge command was issued at the earliest possible time without violating t_RAS(min). The user
must not issue another command to the same bank until the precharge (t_RP) is completed.
The NTC DDR SDRAM devices supports the optional t_RAS lockout feature. This feature allows a Read command with Auto Pre-
charge to be issued to a bank that has been activated (opened) but has not yet satisfied the t_RAS(min) specification. The t_RAS
lockout feature essentially delays the onset of the auto precharge operation until two conditions occur. One, the entire burst
length of data has been successfully prefetched from the memory array; and two, t_RAS(min) has been satisfied.
As a means to specify whether a DDR SDRAM device supports the t_RAS lockout feature, a new parameter has been defined,
t_RAP (RAS Command to Read Command with Auto Precharge or better stated Bank Activate to Read Command with Auto Pre-
charge). For devices that support the t_RAS lockout feature, t_RAP = t_RCD(min). This allows any Read Command (with or without
Auto Precharge) to be issued to an open bank once t_RCD(min) is satisfied.
t_RAP Definition
CL=2, t_CK=10ns
CK
CK
Command NOP
ACT
NOP
RD A
NOP
NOP
NOP
NOP
ACT
NOP
NOP
DQ (BL=2)
DQ0 DQ1
t_RASmin
*
t_RPmin
Command NOP
ACT
NOP
RD A
NOP
NOP
NOP
NOP
ACT
NOP
NOP
DQ (BL=4)
DQ0 DQ1 DQ2 DQ3
*
t_RPmin
Command NOP
ACT
NOP
RD A
NOP
NOP
NOP
NOP
NOP
ACT
NOP
DQ (BL=8)
DQ0 DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7
t_RCDmin
t_RAPmin
*
t_RPmin
*^{Indicates Auto Precharge begins here}
The above timing diagrams show the effects of t_RAP for devices that support t_RAS lockout. In these cases, the Read
with Auto Precharge command (RDA) is issued with t_RCD(min) and dataout is available with the shortest latency from the
Bank Activate command (ACT). The internal precharge operation, however, does not begin until after t_RAS(min) is satisfied.
Burst Terminate
The Burst Terminate command is used to truncate read bursts (with Auto Precharge disabled). The most re-cently registered
Read command prior to the Burst Terminate command is truncated, as shown in the Operation section of this data sheet. Write
burst cycles are not to be terminated with the Burst Terminate command.
REV 1.1
12/2001
17
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