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K4H1G0838M-TCA0 Datasheet

  • K4H1G0838M-TCA0

  • 128Mb DDR SDRAM

  • 53頁(yè)

  • SAMSUNG   SAMSUNG

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128Mb DDR SDRAM
3.3.5 Read Interrupted by a Precharge
A Burst Read operation can be interrupted by precharge of the same bank. The minimum 1 clock is required
for the read to precharge intervals. A precharge command to output disable latency is equivalent to the CAS
latency.
< Burst Length=8, CAS Latency=2 >
0
CK
CK
1t
CK
1
2
3
4
5
6
7
8
Command
DQS
CAS Latency=2
DQ
鈥瞫
READ
Precharge
NOP
NOP
NOP
NOP
NOP
NOP
NOP
Dout 0 Dout 1 Dout 2 Dout 3 Dout 4 Dout 5 Dout 6 Dout 7
Interrupted by precharge
Figure 13. Read interrupted by a precharge timing
When a burst Read command is issued to a DDR SDRAM, a Precharge command may be issued to the same
bank before the Read burst is complete. The following functionality determines when a Precharge command
may be given during a Read burst and when a new Bank Activate command may be issued to the same bank.
1. For the earliest possible Precharge command without interrupting a Read burst, the Precharge command
may be given on the rising clock edge which is CL clock cycles before the end of the Read burst where CL
is the CAS Latency. A new Bank Activate command may be issued to the same bank after tRP (RAS
Precharge time).
2. When a Precharge command interrupts a Read burst operation, the Precharge command may be given on
the rising clock edge which is CL clock cycles before the last data from the interrupted Read burst where
CL is the CAS Latency. Once the last data word has been output, the output buffers are tristated. A new
Bank Activate command may be issued to the same bank after tRP.
3. For a Read with autoprecharge command, a new Bank Activate command may be issued to the same
bank after tRP where tRP begins on the rising clock edge which is CL clock cycles before the end of the
Read burst where CL is the CAS Latency. During Read with autoprecharge, the initiation of the internal
precharge occurs at the same time as the earliest possible external Precharge command would initiate a
precharge operation without interrupting the Read burst as described in 1 above.
4. For all cases above, tRP is an analog delay that needs to be converted into clock cycles. The number of
clock cycles between a Precharge command and a new Bank Activate command to the same bank equals
tRP/tCK (where tCK is the clock cycle time) with the result rounded up to the nearest integer number of
clock cycles. (Note that rounding to X.5 is not possible since the Precharge and Bank Activate commands
can only be given on a
rising
clock edge).
In all cases, a Precharge operation cannot be initiated unless tRAS(min) [minimum Bank Activate to Precharge
time] has been satisfied. This includes Read with autoprecharge commands where tRAS(min) must still be
satisfied such that a Read with autoprecharge command has the same timing as a Read command followed by
the earliest possible Precharge command which does not interrupt the burst.
- 23 -
REV. 1.0 November. 2. 2000

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