AS7C33512PFS16A
AS7C33512PFS18A
®
Functional description
The AS7C33512PFS16A and AS7C33512PFS18A are high performance CMOS 8-Mbit synchronous Static Random Access Memory (SRAM)
devices organized as 524,288 words × 16 or 18 bits and incorporate a pipeline for highest frequency on any given technology.
Fast cycle times of 6/6.6/7.5/10 ns with clock access times (t
CD
) of 3.5/3.8/4.0/5.0 ns enable 166, 150, 133 and 100 MHz bus frequencies.
Three chip enable 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 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 16
or 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 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 select CE0 blocks ADSP, but not ADSC.
The AS7C33512PFS16A and AS7C33512PFS18A operate from a 3.3V 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.
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
= 0V
Max
5
7
Unit
pF
pF
Write enable truth table (per byte)
GWE
L
H
H
H
BWE
X
L
H
L
BWn
X
L
X
H
WEn
T
T
F*
F*
Key: X = don’t care, L = low, H = high, T = true, F = false; * = valid read; n = a,b;
WE, WEn
= internal write signal
Burst order
Interleaved Burst Order LBO=1
A1 A0 A1 A0 A1 A0 A1 A0
Starting Address 0 0
01
10
11
First increment 0 1
00
11
10
Second increment 1 0
11
00
01
Third increment 1 1
10
01
00
Linear Burst Order LBO=0
A1 A0 A1 A0 A1 A0 A1 A0
Starting Address 0 0
01
10
11
First increment 0 1
10
11
00
Second increment 1 0
11
00
01
Third increment 1 1
00
01
10
5/9/03, v.1.8.1
Alliance Semiconductor
2 of 13
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
