AS7C331MPFS18A
®
Functional description
The AS7C331MPFS18A is a high-performance CMOS 16-Mbit synchronous Static Random Access Memory (SRAM) device organized as
1,048,576 words X 18 bits and incorporates a two-stage register-register pipeline for highest frequency on any given technology.
Fast cycle times of 4/4.4/5/6 ns with clock access times (t
CD
) of 2.6/2.8/3/3.4 ns enable 250, 225, 200, and 166 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 is 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 it 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 mode is selectable with the LBO input. With LBO unconnected or driven high, burst operations use an interleaved count
sequence. With LBO driven low, the device uses a linear count sequence.
Write cycles are performed by disabling the output buffers with OE and asserting a write command. A global write enable GWE writes all
18 bits regardless of the state of individual BW[a,b] inputs. Alternately, when GWE is high, one or more bytes may be written by asserting
BWE and the appropriate individual byte BWn signals.
BWn is ignored on the clock edge that samples ADSP low, but it 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.
The AS7C331MPFS18A 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 TQFP and 165-ball BGA.
TQFP and BGA capacitance
Parameter
Input capacitance
I/O capacitance
Symbol
C
IN
C
I/O
Signals
Address and control pins
I/O pins
Test conditions
V
IN
= 0V
V
IN
= V
OUT
Max
5
7
Unit
pF
pF
12/2/02, v. 0.9.2 Advance Info
Alliance Semiconductor
3 of 21
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
