IBM0612404GT3B
IBM0612804GT3B
128Mb Double Data Rate Synchronous DRAM
Advance Rev 0.2
t
and t
Definition
RCD
RRD
CK
CK
RD/WR
ACT
NOP
ACT
NOP
NOP
NOP
NOP
Command
A0-A11
ROW
BA x
ROW
BA y
COL
BA y
BA0, BA1
t
t
RCD
RRD
Don’t Care
Reads
Subsequent to programming the mode register with CAS latency, burst type, and burst length, Read bursts
are initiated with a Read command.
The starting column and bank addresses are provided with the Read command and Auto Precharge is either
enabled or disabled for that burst access. If Auto Precharge is enabled, the row that is accessed starts pre-
charge at the completion of the burst, provided t
has been satisfied. For the generic Read commands
RAS
used in the following illustrations, Auto Precharge is disabled.
During Read bursts, the valid data-out element from the starting column address is available following the
CAS latency after the Read command. Each subsequent data-out element is valid nominally at the next posi-
tive or negative clock edge (i.e. at the next crossing of CK and CK). The following timing figure entitled “Read
Burst: CAS Latencies (Burst Length=4)” illustrates the general timing for each supported CAS latency setting.
DQS is driven by the DDR SDRAM along with output data. The initial low state on DQS is known as the read
preamble; the low state coincident with the last data-out element is known as the read postamble. Upon com-
pletion of a burst, assuming no other commands have been initiated, the DQs and DQS goes High-Z. Data
from any Read burst may be concatenated with or truncated with data from a subsequent Read command. In
either case, a continuous flow of data can be maintained. The first data element from the new burst follows
either the last element of a completed burst or the last desired data element of a longer burst which is being
truncated. The new Read command should be issued x cycles after the first Read command, where x equals
the number of desired data element pairs (pairs are required by the 2n prefetch architecture). This is shown in
timing figure entitled “Consecutive Read Bursts: CAS Latencies (Burst Length =4 or 8)”. A Read command
can be initiated on any positive clock cycle following a previous Read command. Nonconsecutive Read data
is shown in timing figure entitled “Non-Consecutive Read Bursts: CAS Latencies (Burst Length = 4)”. Full-
speed Random Read Accesses: CAS Latencies (Burst Length = 2, 4 or 8) within a page (or pages) can be
performed as shown on page 25.
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Use is further subject to the provisions at the end of this document.
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