6.422
IDT71P71204 (2M x 8-Bit), 71P71104 (2M x 9-Bit), 71P71804 (1M x 18-Bit) 71P71604 (512K x 36-Bit)
Advance Information
18 Mb DDR II SRAM Burst of 2 Commercial Temperature Range
signals can be used to prevent writing any byte or individual nibbles,
or combined to prevent writing one word of the burst. The x18 and
x36 DDRll devices have the ability to address to the individual word
level using the SA0 address, but the burst will continue in a linear
sequence and wrap back on itself. The address will not increment to
the next higher burst address location, but instead will return to it’s
own lower words within the burst location. Similarly when reading x18
and x36 DDRll devices, the read burst will begin at the designated
address, but if the burst is started at any other position than the first
word of the burst, the burst will wrap back on itself and read the first
locations before completing.
Output Enables
The DDRII SRAM automatically enables and disables the DQ[X:0]
outputs. When a valid read is in progress, and data is present at the
output, the output will be enabled. If no valid data is present at the output
(read not active), the output will be disabled (high impedance). The
echo clocks will remain valid at all times and cannot be disabled or turned
off. During power-up the DQ outputs will come up in a high impedance
state.
Programmable Impedance
An external resistor, RQ, must be connected between the ZQ pin on
the SRAM and Vss to allow the SRAM to adjust its output drive imped-
ance. The value of RQ must be 5X the value of the intended drive
impedance of the SRAM. The allowable range of RQ to guarantee
impedance matching with a tolerance of +/- 10% is between 175 ohms
and 350 ohms, with VDDQ = 1.5V. The output impedance is adjusted
every 1024 clock cycles to correct for drifts in supply voltage and tem-
perature. If the user wishes to drive the output impedance of the SRAM
to it’s lowest value, the ZQ pin may be tied to VDDQ.
The C and C clocks may be used to clock the data out of the output
register during read operations and to generate the echo clocks. C and
C must be presented to the SRAM within the timing tolerances. The
output data from the DDRII will be closely aligned to the C and C input,
through the use of an internal DLL. When C is presented to the DDRII
SRAM, the DLL will have already internally clocked the first data word to
arrive at the device output simultaneously with the arrival of the C clock.
The C and second data word of the burst will also correspond.
Single Clock Mode
The DDRII SRAM may be operated with a single clock pair. C and C
may be disabled by tying both signals high, forcing the outputs and echo
clocks to be controlled instead by the K and K clocks.
DLL Operation
The DLL in the output structure of the DDRII SRAM can be used to
closely align the incoming clocks C and C with the output of the data,
generating very tight tolerances between the two. The user may disable
the DLL by holding Doff low. With the DLL off, the C and C (or K and K
if C and C are not used) will directly clock the output register of the SRAM.
With the DLL off, there will be a propagation delay from the time the clock
enters the device until the data appears at the output.
Echo Clock
The echo clocks, CQ and CQ, are generated by the C and C clocks
(or K, K if C, C are disabled). The rising edge of C generates the rising
edge of CQ, and the falling edge of CQ. The rising edge of C generates
the rising edge of CQ and the falling edge of CQ. This scheme improves
the correlation of the rising and falling edges of the echo clock and will
improve the duty cycle of the individual signals.
The echo clock is very closely aligned with the data, guaranteeing that
the echo clock will remain closely correlated with the data, within the
tolerances designated.
Read and Write Operations
Read operations are initiated by holding Read/Write control input
(R/W) high, the load control input (LD) low and presenting the read
address to the address port during the rising edge of K, which will latch
the address. The data will then be read and will appear at the device
output at the designated time in correspondence with the C and C clocks.
Write operations are initiated by holding the Read/Write control input
(R/W) low, the load control input (LD) low and presenting the write
address to the address port during the rising edge of K, which will latch
the address. On the following rising edge of K, the first word of the two
word burst must be present on the data input bus DQ[x:O], along with the
appropriate byte write or nibble write (BW or NW) inputs. On the follow-
ing rising edge of K, the second half of the data write burst will be
accepted at the device input with the designated (BW or NW) inputs.
DDRII devices internally store two words of the burst as a single,
wide word and will retain their order in the burst. The x8 and x9
DDRII devices do not have the ability to address to the single word
level or reverse the burst order; however the byte and nibble write
The K clock is used to clock in the control signals (BWx or NWx), and the
second word of the data burst during a write operation. The K and K
clocks are also used internally by the SRAM. In the event that the user
disables the C and C clocks, the K and K clocks will also be used to clock
the data out of the output register and generate the echo clocks.
