®
AS7C33256PFS32A
AS7C33256PFS36A
12/12/00 ALLIANCE SEMICONDUCTOR 2
Functional description
The AS7C33256PFS32A and AS7C33256PFS36A are high-performance CMOS 8-Mbit synchronous Static Random Access Memory (SRAM)
devices organized as 262,144 words x 32 or 36 bits, and incorporate a two-stage register-register pipeline for highest frequency on any
given technology.
Timing for these devices is compatible with existing Pentium
®
synchronous cache specifications. This architecture is suited for ASIC, DSP
(TMS320C6X), and PowerPC
™
*
-based systems in computing, datacomm, instrumentation, and telecommunications systems.
Fast cycle times of 6/6.7/7.5/10 ns with clock access times (t
CD
) of 3.5/3.8/4.0/5.0 ns enable 167, 150, 133 and 100 MHz bus
frequencies. Three chip enable (CE
) inputs permit easy memory expansion. Burst operation is initiated in one of two ways: the controller
address strobe (ADSC
), or the processor address strobe (ADSP). The burst advance pin (ADV) allows subsequent internally generated burst
addresses.
Read cycles are initiated with ADSP
(regardless of WE and ADSC) using the new external address clocked into the on-chip address register
when ADSP
is sampled Low, the chip enables are sampled active, and the output buffer is enabled with OE. In a read operation the data
accessed by the current address, registered in the address registers by the positive edge of CLK, are carried to the data-out registers and driven
on the output pins on the next positive edge of CLK. ADV
is ignored on the clock edge that samples ADSP asserted, but is sampled on all
subsequent clock edges. Address is incremented internally for the next access of the burst when ADV
is sampled Low, and both address
strobes are High. Burst operation is selectable with the LBO
input. With LBO unconnected or driven High, burst operations use a Pentium
®
count sequence. With LBO driven LOW, the device uses a linear count sequence suitable for PowerPC™ and many other applications.
Write cycles are performed by disabling the output buffers with OE
and asserting a write command. A global write enable GWE writes all
32/36bits regardless of the state of individual BW[a:d]
inputs. Alternately, when GWE is High, one or more bytes may be written by
asserting BWE
and the appropriate individual byte BWn signal(s).
BWn
is ignored on the clock edge that samples ADSP Low, but is sampled on all subsequent clock edges. Output buffers are disabled when
BWn
is sampled LOW (regardless of OE). Data is clocked into the data input register when BWn is sampled Low. Address is incremented
internally to the next burst address if BWn
and ADV are sampled Low.
Read or write cycles may also be initiated with ADSC
instead of ADSP. The differences between cycles initiated with ADSC and ADSP follow.
• ADSP
must be sampled HIGH when ADSC is sampled LOW to initiate a cycle with ADSC.
• WE
signals are sampled on the clock edge that samples ADSC LOW (and ADSP High).
• Master chip enable CE0
blocks ADSP, but not ADSC.
AS7C33256PFS32A and AS7C33256PFS36A family operates from a core 3.3V power supply. I/Os use a separate power supply that can
operate at 2.5V or 3.3V. These devices are available in a 100-pin 14 × 20 mm TQFP package.
*PowerPC™ is a tradenark International Business Machines Corporation.
Capacitance
Write enable truth table (per byte)
Key:
X = Don’t Care, L = Low, H = High, T = True, F = False; *= Valid read; n = a, b, c, d; WE, WEn = internal write signal.
Parameter Symbol Signals Test conditions Max Unit
Input capacitance C
IN
Address and control pins VIN = 0V 5 pF
I/O capacitance C
I/O
I/O pins VIN = V
OUT
= 0V 7 pF
GWE
BWE BWn WEn
L X X T
H L L T
H H X F*
H L H F
*