IDT71P72204 (2M x 8-Bit), 71P72104 (2M x 9-Bit), 71P72804 (1M x 18-Bit) 71P72604 (512K x 36-Bit)
18 Mb QDR II SRAM Burst of 2
Commercial Temperature Range
that is precisely timed to the data output, and tuned with matching imped-
ance and signal quality. The user can use the echo clock for down-
stream clocking of the data. Echo clocks eliminate the need for the user
to produce alternate clocks with precise timing, positioning, and signal
qualities to guarantee data capture. Since the echo clocks are generated
by the same source that drives the data output, the relationship to the data
is not significantly affected by voltage, temperature and process, as would
be the case if the clock were generated by an outside source.
All interfaces of the QDRII SRAM are HSTL, allowing speeds beyond
SRAM devices that use any form of TTL interface. The interface can be
scaled to higher voltages (up to 1.9V) to interface with 1.8V systems if
necessary. The device has a VDDQ and a separate Vref, allowing the
user to designate the interface operational voltage, independent of the
device core voltage of 1.8V VDD. The output impedance control allows
the user to adjust the drive strength to adapt to a wide range of loads and
The device is capable of sustaining full bandwidth on both the input
and output ports simultaneously. All data is in two word bursts, with
addressing capability to the burst level.
The QDRII SRAM has two sets of input clocks, namely the K, K clocks
and the C, C clocks. In addition, the QDRII has an output “echo” clock,
The K and K clocks are the primary device input clocks. The K clock
is, used to clock in the control signals (R, W and BWx or NWx), the read
address, and the first word of the data burst during a write operation.
The K clock is used to clock in the control signals (BWx or NWx), write
address 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
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 QDRII will be closely aligned to the C and C input,
through the use of an internal DLL. When C is presented to the QDRII
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 QDRII 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.
The DLL in the output structure of the QDRII 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.
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
Read and Write Operations
QDRII devices internally store the two words of the burst as a single,
wide word and will retain their order in the burst. There is no ability to
address to the single word level or reverse the burst order; however, the
byte and nibble write signals can be used to prevent writing any indi-
vidual bytes, or combined to prevent writing one word of the burst.
Read operations are initiated by holding the read port select (R) 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 write port select (W) low
and designating with the Byte Write inputs (BWx) which bytes are to be
written (or NWx on x8 devices). The first word of the data must also be
present on the data input bus D[X:0]. Upon the rising edge of K the first
word of the burst will be latched into the input register. After K has risen,
and the designated hold times observed, the second half of the clock
cycle is initiated by presenting the write address to the address bus
SA[X:0], the BWx (or NWx) inputs for the second data word of the burst,
and the second data item of the burst to the data bus D[X:0]. Upon the
rising edge of K, the second word of the burst will be latched, along with
the designated address. Both the first and second words of the burst will
then be written into memory as designated by the address and byte write
The QDRII SRAM automatically enables and disables the Q[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 Q outputs will come up in a high 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.