A48P3616 Datasheet, PDF (20/62 Pages) AMIC Technology – 8M X 16 Bit DDR DRAM

A48P3616
Preliminary
Device Operations
Deselect
The Deselect function prevents new commands from being
executed by the DDR SDRAM. The DDR SDRAM is
effectively deselected. Operations already in progress are not
affected.
No Operation (NOP)
The No Operation (NOP) command is used to perform a NOP
to a DDR SDRAM. This prevents unwanted commands from
being registered during idle or wait states. Operations already
in progress are not affected.
Mode Register Set
The mode registers are loaded via inputs A0-A11, BA0 and
BA1 while issuing the Mode Register Set Command. See
mode register descriptions in the Register Definition section.
The Mode Register Set command can only be issued when
all banks are idle and no bursts are in progress. A subsequent
executable command cannot be issued until tMRD is met.
Active
The Active command is used to open (or activate) a row in a
particular bank for a subsequent access. The value on the
BA0, BA1 inputs selects the bank, and the address provided
on inputs A0-A11 selects the row. This row remains active (or
open) for accesses until a Precharge (or Read or Write with
Auto Precharge) is issued to that bank. A Precharge (or Read
or Write with Auto Precharge) command must be issued and
completed before opening a different row in the same bank.
Read
The Read command is used to initiate a burst read access to
an active (open) row. The value on the BA0, BA1 inputs
selects the bank, and the address provided on inputs A0-A8
selects the starting column location. The value on input A10
determines whether or not Auto Precharge is used. If Auto
Precharge is selected, the row being accessed is precharged
at the end of the Read burst; if Auto Precharge is not selected,
the row remains open for subsequent accesses.
Write
The Write command is used to initiate a burst write access to
an active (open) row. The value on the BA0, BA1 inputs
selects the bank, and the address provided on inputs A0-A8
selects the starting column location. The value on input A10
determines whether or not Auto Precharge is used. If Auto
Precharge is selected, the row being accessed is precharged
at the end of the Write burst; if Auto Precharge is not selected,
the row remains open for subsequent accesses. Input data
appearing on the DQs is written to the memory array subject
to the DM input logic level appearing coincident with the data.
If a given DM signal is registered low, the corresponding data
is written to memory; if the DM signal is registered high, the
corresponding data inputs are ignored, and a Write is not
executed to that byte/column location.
8M X 16 Bit DDR DRAM
Precharge
The Precharge command is used to deactivate (close) the
open row in a particular bank or the open row(s) in all banks.
The bank(s) will be available for a subsequent row access a
specified time (tRP) after the Precharge command is issued.
Input A10 determines whether one or all banks are to be
precharged, and in the case where only one bank is to be
precharged, inputs BA0, BA1 select the bank. Otherwise BA0,
BA1 are treated as “Don’t Care.” Once a bank has been
precharged, it is in the idle state and must be activated prior
to any Read or Write commands being issued to that bank. A
precharge command is treated as a NOP if there is no open
row in that bank, or if the previously open row is already in the
process of precharging.
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 non-persistent 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 tRAS(min).
The user must not issue another command to the same bank
until the precharge (tRP) is completed.
The NTC DDR SDRAM devices supports the optional tRAS
lockout feature. This feature allows a Read command with
Auto Precharge to be issued to a bank that has been
activated (opened) but has not yet satisfied the tRAS(min)
specification. The tRAS 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,
tRAS(min) has been satisfied.
As a means to specify whether a DDR SDRAM device
supports the tRAS lockout feature, a new parameter has been
defined, tRAP (RAS Command to Read Command with Auto
Precharge or better stated Bank Activate to Read Command
with Auto Precharge). For devices that support the tRAS
lockout feature, tRAP = tRCD(min). This allows any Read
Command (with or without Auto Precharge) to be issued to an
open bank once tRCD(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.
Preliminary (September 2005, Version 0.0)
19
AMIC Technology, Corp.