參數資料
型號： IBMN625404GT3B
廠商： IBM Microeletronics
英文描述： 256Mb Double Data Rate Synchronous DRAM(256M位雙數據速率同步動態(tài)RAM)
中文描述： 256MB雙數據速率同步DRAM（256M位雙數據速率同步動態(tài)RAM）的
文件頁數： 17/79頁
文件大小： 1328K
代理商： IBMN625404GT3B
IBMN625404GT3B
IBMN625804GT3B
Preliminary
256Mb Double Data Rate Synchronous DRAM
29L0011.E36997B
1/01
IBM Corporation. All rights reserved.
Use is further subject to the provisions at the end of this document.
Page 17 of 79
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 Pre-
charge 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 deter-
mined 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 com-
pleted.
The IBM DDR SDRAM devices supports the optional t
RAS
lockout feature. This feature allows a Read com-
mand with Auto Precharge 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 oper-
ation 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 Acti-
vate to Read Command with Auto Precharge). 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
CK
CK
Command
DQ (BL=2)
t
RAPmin
NOP
ACT
NOP
RD A
NOP
NOP
NOP
NOP
ACT
NOP
NOP
t
RCDmin
t
RASmin
DQ0
DQ1
The above timing diagrams show the effects of t
for devices that support t
with Auto Precharge command (RDA) is issued with t
(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.
CL=2, t
CK
=10ns
Command
DQ (BL=4)
NOP
ACT
NOP
RD A
NOP
NOP
NOP
*
NOP
ACT
NOP
NOP
DQ0
DQ1
DQ2
DQ3
t
RPmin
Command
DQ (BL=8)
NOP
ACT
NOP
RD A
NOP
NOP
*
NOP
NOP
ACT
NOP
DQ0
DQ1
DQ2
DQ3
DQ4
DQ5
t
RPmin
DQ6
DQ7
*
*
Indicates Auto Precharge begins here
t
RPmin
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