‡ PRODUCTS AND SPECIFICATIONS DISCUSSED HEREIN ARE FOR EVALUATION AND REFERENCE PURPOSES ONLY AND ARE
SUBJECT TO CHANGE BY MICRON WITHOUT NOTICE. PRODUCTS ARE ONLY WARRANTED BY MICRON TO MEET MICRON’S
1
2
2
-75Z
-75
-8
PRODUCTION DATA SHEET SPECIFICATIONS.
Configuration32 Meg x 4 x 4 banks16 Meg x 8 x 4 banks 8 Meg x 16 x 4 banks
Refresh Count8K8K8K
Row Addressing8K (A0–A12)8K (A0–A12)8K (A0–A12)
Bank Addressing4 (BA0, BA1)4 (BA0, BA1)4 (BA0, BA1)
Column Addressing4K (A0–A9, A11, A12)2K (A0–A9, A1 1)1K (A0–A9)
KEY TIMING PARAMETERS
SPEEDCLOCK RATEDATA-OUTACCESSDQS-DQ
GRADECL = 2**CL = 2.5**WINDOW* WINDOWSKEW
-75133 MHz133 MHz2.5ns±0.75ns+0.5ns
-75100 MHz133 MHz2.5ns±0.75ns+0.5ns
-8100 MHz125 MHz3.4ns±0.8ns+0.6ns
*Minimum clock rate @ CL = 2 (-8) and CL = 2.5 (-75)
**CL = CAS (Read) Latency
1
128 Meg x 464 Meg x 832 Meg x 16
ADVANCE
512Mb: x4, x8, x16
DDR SDRAM
512Mb DDR SDRAM PART NUMBERS
(Note: xx= -75, -75Z, or -8)
PART NUMBERCONFIGURATIONI/O DRIVE LEVELREFRESH OPTION
MT46V128M4TG-xx128 Meg x 4Full DriveStandard
MT46V128M4TG-xxL128 Meg x 4Full DriveLow Power
MT46V64M8TG-xx64 Meg x 8Full DriveStandard
MT46V64M8TG-xxL64 Meg x 8Full DriveLow Power
MT46V32M16TG-xx32 Meg x 16Programmable DriveStandard
MT46V32M16TG-xxL32 Meg x 16Programmable DriveLow Power
GENERAL DESCRIPTION
The 512Mb DDR SDRAM is a high-speed CMOS,
dynamic random-access memory containing
536,870,912 bits. It is internally configured as a quadbank DRAM.
The 512Mb DDR SDRAM uses a double data rate
architecture to achieve high-speed operation. The
double data rate architecture is essentially a 2n-
prefetch architecture with an interface designed to
transfer two data words per clock cycle at the I/O pins.
A single read or write access for the 512Mb DDR SDRAM
effectively consists of a single 2n-bit wide, one-clockcycle data transfer at the internal DRAM core and two
corresponding n-bit wide, one-half-clock-cycle data
transfers at the I/O pins.
A bidirectional data strobe (DQS) is transmitted externally, along with data, for use in data capture at the
receiver. DQS is a strobe transmitted by the DDR
SDRAM during READs and by the memory controller
during WRITEs. DQS is edge-aligned with data for
READs and center-aligned with data for WRITEs. The
x16 offering has two data strobes, one for the lower byte
and one for the upper byte.
The 512Mb DDR SDRAM operates from a differential clock (CK and CK#); the crossing of CK going HIGH
and CK# going LOW will be referred to as the positive
edge of CK. Commands (address and control signals)
are registered at every positive edge of CK. Input data
is registered on both edges of DQS, and output data is
referenced to both edges of DQS, as well as to both
edges of CK.
Read and write accesses to the DDR SDRAM are
burst oriented; accesses start at a selected location and
continue for a programmed number of locations in a
programmed sequence. Accesses begin with the regis-
tration of an ACTIVE command, which is then followed
by a READ or WRITE command. The address bits registered coincident with the ACTIVE command are used
to select the bank and row to be accessed. The address
bits registered coincident with the READ or WRITE command are used to select the bank and the starting column location for the burst access.
The DDR SDRAM provides for programmable READ
or WRITE burst lengths of 2, 4, or 8 locations. An auto
precharge function may be enabled to provide a selftimed row precharge that is initiated at the end of the
burst access.
As with standard SDR SDRAMs, the pipelined,
multibank architecture of DDR SDRAMs allows for concurrent operation, thereby providing high effective
bandwidth by hiding row precharge and activation
time.
An auto refresh mode is provided, along with a
power-saving power-down mode. All inputs are compatible with the JEDEC Standard for SSTL_2. All full
drive strength outputs are SSTL_2, Class II compatible.
NOTE: 1. The functionality and the timing specifications
discussed in this data sheet are for the DLL-enabled
mode of operation.
2. Throughout the data sheet, the various figures and
text refer to DQs as “DQ.” The DQ term is to be
interpreted as any and all DQ collectively, unless
specifically stated otherwise. Additionally, the x16 is
divided in to two bytes—the lower byte and upper
byte. For the lower byte (DQ0 through DQ7) DM
refers to LDM and DQS refers to LDQS; and for the
upper byte (DQ8 through DQ15) DM refers to UDM
and DQS refers to UDQS.
45, 46CK, CK#InputClock: CK and CK# are differential clock inputs. All address and
control input signals are sampled on the crossing of the positive
edge of CK and negative edge of CK#. Output data (DQs and
DQS) is referenced to the crossings of CK and CK#.
44CKEInputClock Enable: CKE HIGH activates and CKE LOW deactivates the
internal clock, input buffers and output drivers. Taking CKE LOW
provides PRECHARGE POWER-DOWN and SELF REFRESH
operations (all banks idle), or ACTIVE POWER-DOWN (row
ACTIVE in any bank). CKE is synchronous for POWER-DOWN
entry and exit, and for SELF REFRESH entry. CKE is asynchronous
for SELF REFRESH exit and for disabling the outputs. CKE must be
maintained HIGH throughout read and write accesses. Input
buffers (excluding CK, CK# and CKE) are disabled during POWERDOWN. Input buffers (excluding CKE) are disabled during SELF
REFRESH. CKE is an SSTL_2 input but will detect an LVCMOS
LOW level after VDD is applied.
24CS#InputChip Select: CS# enables (registered LOW) and disables (regis-
tered HIGH) the command decoder. All commands are masked
when CS# is registered HIGH. CS# provides for external bank
selection on systems with multiple banks. CS# is considered part
of the command code.
23, 22, 21RAS#, CAS#,InputCommand Inputs: RAS#, CAS#, and WE# (along with CS#) define the
WE#command being entered.
47 DMInputInput Data Mask: DM is an input mask signal for write data. Input
20, 47LDM, UDMdata is masked when DM is sampled HIGH along with that input data
during a WRITE access. DM is sampled on both edges of DQS.
Although DM pins are input-only, the DM loading is designed to
match that of DQ and DQS pins. For the x16 , LDM is DM for DQ0DQ7 and UDM is DM for DQ8-DQ15. Pin 20 is a NC on x4 and x8
26, 27BA0, BA1InputBank Address Inputs: BA0 and BA1 define to which bank an
ACTIVE, READ, WRITE, or PRECHARGE command is being applied.
29-32, 35-40,A0–A12InputAddress Inputs: Provide the row address for ACTIVE commands, and
28, 41, 42the column address and auto precharge bit (A10) for READ/WRITE
commands, to select one location out of the memory array in the
respective bank. A10 sampled during a PRECHARGE command
determines whether the PRECHARGE applies to one bank (A10 LOW,
bank selected by BA0, BA1) or all banks (A10 HIGH). The address
inputs also provide the op-code during a MODE REGISTER SET
command. BA0 and BA1 define which mode register (mode register
or extended mode register) is loaded during the LOAD MODE
REGISTER command.
2, 4, 5, 7, 8, 10, 11, 13,DQ0–15I/OData Input/Output: Data bus for x16 (4, 7, 10, 13, 54, 57, 60, and 63
54, 56, 57, 59, 60, 62,are NC for x8), (2, 4, 7, 8,10, 13, 54, 57, 59, 60, 63, and 65 for x4).
2, 5, 8, 11, 56, 59, 62, 65DQ0-7I/OData Input/Output: Data bus for x8 (2, 8, 59 and 65 are NC for x4).
5, 11, 56, 62DQ0-3I/OData Input/Output: Data bus for x4.
51DQSI/OData Strobe: Output with read data, input with write data. DQS is
16, 51LDQS, UDQS edge-aligned with read data, centered in write data. It is used to
capture data. For the x16 , LDQS is DQS for DQ0-DQ7 and UDQS is
DQS for DQ8-DQ15. Pin 16 is NC on x4 and x8.
50DNU–Do Not Use: Must float to minimize noise.
3, 9, 15, 55, 61V
6, 12, 52, 58, 64VSSQSupplyDQ Ground. Isolated on the die for improved noise immunity.
1, 18, 33VDDSupplyPower Supply: +2.5V ±0.2V.
34, 48, 66VSSSupplyGround.
49VREFSupplySSTL_2 reference voltage.
14, 17, 19, 25, 43, 53NC–No Connect: These pins should be left unconnected.
DDQSupplyDQ Power Supply: +2.5V ±0.2V. Isolated on the die for improved
noise immunity.
RESERVED NC PINS
TSOP PIN NUMBERSSYMBOLTYPEDESCRIPTION
17A13IAddress input for 1Gb devices.
NOTE: 1. NC pins not listed may also be reserved for other uses now or in the future. This table simply defines specific NC pins
deemed to be of importance.
The 512Mb DDR SDRAM is a high-speed CMOS,
dynamic random-access memory containing
536,870,912 bits. The 512Mb DDR SDRAM is internally
configured as a quad-bank DRAM.
The 512Mb DDR SDRAM uses a double data rate
architecture to achieve high-speed operation. The
double data rate architecture is essentially a 2n-
prefetch architecture, with an interface designed to
transfer two data words per clock cycle at the I/O pins.
A single read or write access for the 512Mb DDR SDRAM
consists of a single 2n-bit wide, one-clock-cycle data
transfer at the internal DRAM core and two corresponding n-bit wide, one-half-clock-cycle data transfers at
the I/O pins.
Read and write accesses to the DDR SDRAM are
burst oriented; accesses start at a selected location and
continue for a programmed number of locations in a
programmed sequence. Accesses begin with the registration of an ACTIVE command, which is then followed
by a READ or WRITE command. The address bits registered coincident with the ACTIVE command are used
to select the bank and row to be accessed (BA0, BA1
select the bank; A0-A12 select the row). The address
bits registered coincident with the READ or WRITE command are used to select the starting column location
for the burst access.
Prior to normal operation, the DDR SDRAM must be
initialized. The following sections provide detailed information covering device initialization, register definition, command descriptions and device operation.
Initialization
DDR SDRAMs must be powered up and initialized
in a predefined manner. Operational procedures other
than those specified may result in undefined operation. Power must first be applied to VDD and VDDQ simultaneously, and then to VREF (and to the system VTT). VTT
must be applied after VDDQ to avoid device latch-up,
which may cause permanent damage to the device.
VREF can be applied any time after VDDQ but is expected
to be nominally coincident with VTT. Except for CKE,
inputs are not recognized as valid until after VREF is
applied. CKE is an SSTL_2 input but will detect an
LVCMOS LOW level after VDD is applied. Maintaining
an LVCMOS LOW level on CKE during power-up is required to ensure that the DQ and DQS outputs will be
in the High-Z state, where they will remain until driven
in normal operation (by a read access). After all power
supply and reference voltages are stable, and the clock
is stable, the DDR SDRAM requires a 200µs delay prior
to applying an executable command.
Once the 200µs delay has been satisfied, a DESE-
ADVANCE
512Mb: x4, x8, x16
DDR SDRAM
LECT or NOP command should be applied, and CKE
should be brought HIGH. Following the NOP command,
a PRECHARGE ALL command should be applied. Next
a LOAD MODE REGISTER command should be issued
for the extended mode register (BA1 LOW and BA0
HIGH) to enable the DLL, followed by another LOAD
MODE REGISTER command to the mode register (BA0/
BA1 both LOW) to reset the DLL and to program the
operating parameters. Two-hundred clock cycles are
required between the DLL reset and any READ command. A PRECHARGE ALL command should then be
applied, placing the device in the all banks idle state.
Once in the idle state, two AUTO REFRESH cycles
must be performed (tRFC must be satisfied.) Additionally, a LOAD MODE REGISTER command for the mode
register with the reset DLL bit deactivated (i.e., to program operating parameters without resetting the DLL)
is required. Following these requirements, the DDR
SDRAM is ready for normal operation.
Register Definition
MODE REGISTER
The mode register is used to define the specific
mode of operation of the DDR SDRAM. This definition
includes the selection of a burst length, a burst type, a
CAS latency and an operating mode, as shown in Figure 1. The mode register is programmed via the MODE
REGISTER SET command (with BA0 = 0 and BA1 = 0)
and will retain the stored information until it is programmed again or the device loses power (except for
bit A8, which is self-clearing).
Reprogramming the mode register will not alter the
contents of the memory, provided it is performed correctly. The mode register must be loaded (reloaded)
when all banks are idle and no bursts are in progress,
and the controller must wait the specified time before
initiating the subsequent operation. Violating either
of these requirements will result in unspecified operation.
Mode register bits A0-A2 specify the burst length,
A3 specifies the type of burst (sequential or interleaved), A4-A6 specify the CAS latency, and A7-A12
specify the operating mode.
Burst Length
Read and write accesses to the DDR SDRAM are
burst oriented, with the burst length being programmable, as shown in Figure 1. The burst length determines the maximum number of column locations that
can be accessed for a given READ or WRITE command.
Burst lengths of 2, 4, or 8 locations are available for both
Reserved states should not be used, as unknown
operation or incompatibility with future versions may
result.
When a READ or WRITE command is issued, a block
of columns equal to the burst length is effectively selected. All accesses for that burst take place within this
block, meaning that the burst will wrap within the block
if a boundary is reached. The block is uniquely selected by A1-Ai when the burst length is set to two, by
A2-Ai when the burst length is set to four and by A3-Ai
when the burst length is set to eight (where Ai is the
most significant column address bit for a given con-
0
0
-
A7
7
M6
M9M10M12 M11
0
0
0
0
-
-
A6 A5 A4
654
M4
M5
0
0
0
1
0
0
0
1
0
1
1
0
0
0
1
1
0
1
0
1
1
1
1
1
M7
M8
0
0
1
0
-
-
A3A8A2A1A0
38210
Burst LengthCAS Latency BT0*
M1
M0
M2
0
0
0
0
1
0
1
0
0
1
1
0
0
0
1
0
1
1
1
0
1
1
1
1
M3
0
1
M6-M0
Valid
Valid
-
Burst Type
Sequential
Interleaved
CAS Latency
Reserved
Reserved
2
Reserved
Reserved
Reserved
2.5
Reserved
Operating Mode
Normal Operation
Normal Operation/Reset DLL
All other states reserved
Address Bus
Mode Register (Mx)
Burst Length
M3 = 0
Reserved
Reserved
Reserved
Reserved
Reserved
M3 = 1
Reserved
2
4
8
2
4
8
Reserved
Reserved
Reserved
Reserved
BA1
BA0
130*14
* M14 and M13 (BA0 and BA1)
must be “0, 0” to select the
base mode register (vs. the
extended mode register).
A10
A12 A11
11
10
12
Operating Mode
A9
9
0
0
-
Figure 1
Mode Register Definition
figuration). The remaining (least significant) address
bit(s) is (are) used to select the starting location within
the block. The programmed burst length applies to
both READ and WRITE bursts.
Burst Type
Accesses within a given burst may be programmed
to be either sequential or interleaved; this is referred to
as the burst type and is selected via bit M3.
The ordering of accesses within a burst is determined by the burst length, the burst type and the starting column address, as shown in Table 1.
Table 1
Burst Definition
BurstStarting ColumnOrder of Accesses Within a Burst
The READ latency is the delay, in clock cycles, between the registration of a READ command and the
availability of the first bit of output data. The latency
can be set to 2, or 2.5 clocks, as shown in Figure 2.
If a READ command is registered at clock edge n,
and the latency is m clocks, the data will be available
nominally coincident with clock edge n + m. Table 2
indicates the operating frequencies at which each CAS
latency setting can be used.
Reserved states should not be used as unknown
operation or incompatibility with future versions may
result.
CK#
CK
COMMAND
DQS
DQ
CK#
CK
COMMAND
DQS
DQ
T0T1T2T2nT3T3n
READNOPNOPNOP
CL = 2
T0T1T2T2nT3T3n
READNOPNOPNOP
CL = 2.5
Table 2
CAS Latency (CL)
ALLOWABLE OPERATING
FREQUENCY (MHz)
SPEEDCL = 2CL = 2.5
-75Z75 ≤f ≤ 13375 ≤f ≤133
-7575 ≤ f ≤ 10075 ≤f ≤133
-875 ≤ f ≤ 10075 ≤ f ≤125
Operating Mode
The normal operating mode is selected by issuing a
MODE REGISTER SET command with bits A7-A12 each
set to zero, and bits A0-A6 set to the desired values. A
DLL reset is initiated by issuing a MODE REGISTER
SET command with bits A7 and A9-A12 each set to zero,
bit A8 set to one, and bits A0-A6 set to the desired
values. Although not required by the Micron device,
JEDEC specifications recommend when a LOAD MODE
REGISTER command is issued to reset the DLL, it
should always be followed by a LOAD MODE REGISTER command to select normal operating mode.
All other combinations of values for A7-A12 are reserved for future use and/or test modes. Test modes
and reserved states should not be used because unknown operation or incompatibility with future versions may result.
Burst Length = 4 in the cases shown
Shown with nominal tAC and nominal tDSDQ
NOTE: 1. E14 and E13 (BA0 and BA1) must be “1, 0” to select the
Extended Mode Register (vs. the base Mode Register).
2. The reduced drive strength option is not supported on the x4
and x8 versions, and is only available on the x16 version.
3. The QFC# option is not supported.
E2,E3E4
0–0–0–0
–
0
–
E6E5E7E8E9
0–0
–
E10E11
0
–
E12
DS
QFC#
The extended mode register controls functions beyond those controlled by the mode register; these additional functions are DLL enable/disable and
output drive strength. These functions are controlled
via the bits shown in Figure 3. The extended mode
register is programmed via the LOAD MODE REGISTER command to the mode register (with BA0 = 1 and
BA1 = 0) and will retain the stored information until it is
programmed again or the device loses power. The enabling of the DLL should always be followed by a LOAD
MODE REGISTER command to the mode register (BA0/
BA1 both LOW) to reset the DLL.
The extended mode register must be loaded when
all banks are idle and no bursts are in progress, and the
controller must wait the specified time before initiating any subsequent operation. Violating either of these
requirements could result in unspecified operation.
ADVANCE
512Mb: x4, x8, x16
DDR SDRAM
Output Drive Strength
The normal drive strength for all outputs are specified to be SSTL2, Class II. The x16 supports an option
for reduced drive. This option is intended for the support of the lighter load and/or point-to-point environments. The selection of the reduced drive strength will
alter the DQs and DQSs from SSTL2, Class II drive
strength to a reduced drive strength, which is approximately 54% of the SSTL2, Class II drive strength.
The Micron (32Meg x16) device supports a
programmable drive strength option.
DLL Enable/Disable
The DLL must be enabled for normal operation.
DLL enable is required during power-up initialization
and upon returning to normal operation after having
disabled the DLL for the purpose of debug or evaluation. (When the device exits self refresh mode, the DLL
is enabled automatically.) Any time the DLL is enabled,
200 clock cycles must occur before a READ command
can be issued.
Truth Table 1 provides a quick reference of available commands. This is followed by a verbal description of each command. Two additional Truth Tables
TRUTH TABLE 1 – COMMANDS
(Note: 1)
NAME (FUNCTION)CS#RAS#CAS#WE# ADDRNOTES
DESELECT (NOP)HXXX X9
NO OPERATION (NOP)LHHH X9
ACTIVE (Select bank and activate row)LLHHBank/Row3
READ (Select bank and column, and start READ burst)LHLHBank/Col4
WRITE (Select bank and column, and start WRITE burst)LHLLBank/Col4
BURST TERMINATELHHLX8
PRECHARGE (Deactivate row in bank or banks)LLHLCode5
AUTO REFRESH or SELF REFRESHLLLHX6, 7
(Enter self refresh mode)
LOAD MODE REGISTER LLLLOp-Code2
appear following the Operation section; these tables
provide current state/next state information.
TRUTH TABLE 1A – DM OPERATION
(Note: 10)
NAME (FUNCTION)DM DQsNOTES
Write Enable L Valid
Write Inhibit HX
NOTE: 1. CKE is HIGH for all commands shown except SELF REFRESH.
2. BA0-BA1 select either the mode register or the extended mode register (BA0 = 0, BA1 = 0 select the mode register;
BA0 = 1, BA1 = 0 select extended mode register; other combinations of BA0-BA1 are reserved). A0-A12 provide the opcode to be written to the selected mode register.
3. BA0-BA1 provide bank address and A0-A12 provide row address.
4. BA0-BA1 provide bank address; A0-Ai provide column address (where i = 9 for x16, 9,11 for x8, and 9, 11, 12 for x4);
A10 HIGH enables the auto precharge feature (nonpersistent), and A10 LOW disables the auto precharge feature.
5. A10 LOW: BA0-BA1 determine which bank is precharged.
A10 HIGH: all banks are precharged and BA0-BA1 are “Don’t Care.”
6. This command is AUTO REFRESH if CKE is HIGH, SELF REFRESH if CKE is LOW.
7. Internal refresh counter controls row addressing; all inputs and I/Os are “Don’t Care” except for CKE.
8. Applies only to read bursts with auto precharge disabled; this command is undefined (and should not be used) for READ
bursts with auto precharge enabled and for WRITE bursts.
9. DESELECT and NOP are functionally interchangeable.
10. Used to mask write data; provided coincident with the corresponding data.
The DESELECT function (CS# HIGH) 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
instruct the selected DDR SDRAM to perform a NOP
(CS# LOW). This prevents unwanted commands from
being registered during idle or wait states. Operations
already in progress are not affected.
LOAD MODE REGISTER
The mode registers are loaded via inputs A0–A12.
See mode register descriptions in the Register Definition section. The LOAD MODE REGISTER command
can only be issued when all banks are idle, and a subsequent executable command cannot be issued until
t
MRD 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–A12 selects the row.
This row remains active (or open) for accesses until a
PRECHARGE command is issued to that bank.
A PRECHARGE command must be issued before opening a different row in the same bank.
READ
The READ command is used to initiate a burst read
access to an active row. The value on the BA0, BA1
inputs selects the bank, and the address provided on
inputs A0–Ai (where i = 9 for x16; 9, 11 for x8; or 9, 11, and
12 for x4) 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 will be precharged at the end of the READ
burst; if auto precharge is not selected, the row will
remain open for subsequent accesses.
WRITE
The WRITE command is used to initiate a burst write
access to an active row. The value on the BA0, BA1 inputs
selects the bank, and the address provided on inputs
A0–Ai (where i = 9 for x16; 9 and 11 for x8; or 9, 11, and 12
for x4) 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 will be precharged at the end of the WRITE burst;
if auto precharge is not selected, the row will remain
open for subsequent accesses. Input data
ADVANCE
512Mb: x4, x8, x16
DDR SDRAM
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 will be written to memory; if the DM
signal is registered HIGH, the corresponding data inputs will be ignored, and a WRITE will not be executed to
that byte/column location.
PRECHARGE
The PRECHARGE command is used to deactivate
the open row in a particular bank or the open row in
all banks. The bank(s) will be available for a subsequent
row access a specified time (tRP) after the precharge
command is issued. Except in the case of concurrent
auto precharge, where a READ or WRITE command to
a different bank is allowed as long as it does not
interrupt the data transfer in the current bank and does
not violate any other timing parameters. 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
will be treated as a NOP if there is no open row in that
bank (idle state), 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 nonpersistent in that it
is either enabled or disabled for each individual Read or
Write command. This device supports concurrent
auto precharge if the command to the other bank does
not interrupt the data transfer to the current bank.
Auto precharge ensures that the precharge is initiated at the earliest valid stage within a burst. This
“earliest valid stage” is determined as if an explicit
PRECHARGE command was issued at the earliest possible time, without violating tRAS (MIN), as described
for each burst type in the Operation section of this data
sheet. The user must not issue another command to the
same bank until the precharge time (tRP) is completed.
The BURST TERMINATE command is used to truncate READ bursts (with auto precharge disabled). The
most recently registered READ command prior to the
BURST TERMINATE command will be truncated, as
shown in the Operation section of this data sheet. The
open page which the READ burst was terminated from
remains open.
AUTO REFRESH
AUTO REFRESH is used during normal operation of
the DDR SDRAM and is analogous to CAS#-BEFORERAS# (CBR) REFRESH in FPM/EDO DRAMs. This command is nonpersistent, so it must be issued each time
a refresh is required.
The addressing is generated by the internal refresh
controller. This makes the address bits a “Don’t Care”
during an AUTO REFRESH command. The 512Mb DDR
SDRAM requires AUTO REFRESH cycles at an average
interval of 7.8125µs (maximum).
To allow for improved efficiency in scheduling and
switching between tasks, some flexibility in the absolute refresh interval is provided. A maximum of eight
AUTO REFRESH command can be posted to any given
DDR SDRAM, meaning that the maximum absolute
interval between any AUTO REFRESH command and
the next AUTO REFRESH command is 9 × 7.8125µs
(70.3µs). This maximum absolute interval is to allow
ADVANCE
512Mb: x4, x8, x16
DDR SDRAM
future support for DLL updates internal to the DDR
SDRAM to be restricted to AUTO REFRESH cycles, without allowing excessive drift in tAC between updates.
Although not a JEDEC requirement, to provide for
future functionality features, CKE must be active
(High) during the AUTO REFRESH period. The AUTO
REFRESH period begins when the AUTO REFRESH
command is registered and ends tRFC later.
SELF REFRESH
The SELF REFRESH command can be used to retain
data in the DDR SDRAM, even if the rest of the system
is powered down. When in the self refresh mode, the
DDR SDRAM retains data without external clocking.
The SELF REFRESH command is initiated like an AUTO
REFRESH command except CKE is disabled (LOW). The
DLL is automatically disabled upon entering SELF REFRESH and is automatically enabled upon exiting SELF
REFRESH (200 clock cycles must then occur before a
READ command can be issued). Input signals except
CKE are “Don’t Care” during SELF REFRESH.
The procedure for exiting self refresh requires a sequence of commands. First, CK must be stable prior to
CKE going back HIGH. Once CKE is HIGH, the DDR
SDRAM must have NOP commands issued for tXSNR
because time is required for the completion of any internal refresh in progress. A simple algorithm for meeting both refresh and DLL requirements is to apply NOPs
for 200 clock cycles before applying any other command.
Before any READ or WRITE commands can be issued to a bank within the DDR SDRAM, a row in that
bank must be “opened.” This is accomplished via the
ACTIVE command, which selects both the bank and
the row to be activated, as shown in Figure 4.
After a row is opened with an ACTIVE command, a
READ or WRITE command may be issued to that row,
subject to the tRCD specification. tRCD (MIN) should
be divided by the clock period and rounded up to the
next whole number to determine the earliest clock edge
after the ACTIVE command on which a READ or WRITE
command can be entered. For example, a tRCD specification of 20ns with a 133 MHz clock (7.5ns period) results in 2.7 clocks rounded to 3. This is reflected in
Figure 5, which covers any case where 2 < tRCD (MIN)/
t
CK ≤ 3. (Figure 5 also shows the same case for tRCD; the
same procedure is used to convert other specification
limits from time units to clock cycles).
A subsequent ACTIVE command to a different row
in the same bank can only be issued after the previous
active row has been “closed” (precharged). The minimum time interval between successive ACTIVE commands to the same bank is defined by tRC.
A subsequent ACTIVE command to another bank
can be issued while the first bank is being accessed,
which results in a reduction of total row-access overhead. The minimum time interval between successive
ACTIVE commands to different banks is defined by
t
RRD.
CK#
CK
CKE
HIGH
CS#
RAS#
CAS#
WE#
A0-A12
BA0,1
RA
BA
RA = Row Address
BA = Bank Address
Figure 4
Activating a Specific Row in
a Specific Bank
CK#
CK
COMMAND
A0-A12
BA0, BA1
T0T1T2T3T4T5T6T7
ACTACT
RowRow
Bank xBank y
NOP
t
RRD
NOP
NOP
t
RCD
NOP
RD/WR
Col
Bank y
DON’T CARE
NOP
Figure 5
Example: Meeting tRCD (tRRD) MIN When 2 < tRCD (tRRD) MIN/tCK
READ bursts are initiated with a READ command,
as shown in Figure 6.
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 being accessed is
precharged at the completion of the burst. For the generic READ commands used in the following illustrations, auto precharge is disabled.
During READ bursts, the valid data-out element
from the starting column address will be available following the CAS latency after the READ command. Each
subsequent data-out element will be valid nominally
at the next positive or negative clock edge (i.e., at the
next crossing of CK and CK#). Figure 7 shows general
timing for each possible 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 dataout element is known as the read postamble.
Upon completion of a burst, assuming no other commands have been initiated, the DQs will go
High-Z. A detailed explanation of tDQSQ (valid dataout skew), tQH (data-out window hold), the valid data
window are depicted in Figure 27. A detailed explanation of tDQSCK (DQS transition skew to CK) and tAC
(data-out transition skew to CK) is depicted in Figure
28.
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 Figure 8. A READ command can be initiated on any clock cycle following a
previous READ command. Nonconsecutive read data
is shown for illustration in Figure 9. Full-speed random
read accesses within a page (or pages) can be performed
as shown in Figure 10.
CK#
CK
CKE
CS#
RAS#
CAS#
WE#
x4: A0-A9, A11, A12
x8: A0-A9, A11
x16: A0-A9
x8: A12
x16: A11, A12
A10
BA0,1
CA = Column Address
BA = Bank Address
EN AP = Enable Auto Precharge
DIS AP = Disable Auto Precharge