![](http://datasheet.mmic.net.cn/330000/MB81V4260S-60_datasheet_16435911/MB81V4260S-60_5.png)
5
MB81V4260S-60/MB81V4260S-70
I
RECOMMENDED OPERATING CONDITIONS
* :Undershoots of up to –2.0 volts with a pulse width not exceeding 20 ns are acceptable.
I
FUNCTIONAL OPERATION
ADDRESS INPUTS
Eighteen input bits are required to decode any sixteen of 4,194,304 cell addresses in the memory matrix. Since
only nine address bits are available, the column and row inputs are separately strobed by LCAS or UCAS and RAS
as shown in Figure 5. First, nine row address bits are input on pins A
0
-through-A
8
and latched with the row address
strobe (RAS) then, nine column address bits are input and latched with the column address strobe (LCAS or UCAS).
Both row and column addresses must be stable on or before the falling edges of RAS and LCAS or UCAS ,
respectively. The address latches are the flow-through type; thus, address information appearing after t
RAH
(min.)+
t
T
is automatically treated as the column address to start select operation of the column decode. Therefore, to have
correct data within t
RAC
, the column address should be input within t
RAD
(max.). If t
RAD
> t
RAD
(max.), the access time
is the later one of either t
AA
or t
CAS
.
WRITE ENABLE
The read or write mode is determined by the logic state of WE. When WE is active Low, a write cycle is initiated;
when WE is High, a read cycle is selected. During the read mode, input data are ignored. When an early write
cycle is executed, the output buffers stay in a high-impedance state during the cycle.
DATA INPUT
Input data are written into memory in either of three basic ways–the early write cycle, the OE (delayed) write cycle,
and the read-modify-write cycle. The falling edge of WE or LCAS/UCAS, whichever is later, serves as the input
data-latch strobe. In the early write cycle, the input data of DQ
1
-DQ
8
are strobed by LCAS and DQ
9
-DQ
16
are
strobed by UCAS and the setup/hold times are referenced to each falling edge of LCAS and UCAS because WE
goes Low before LCAS/UCAS. In the delayed write or read-modify-write cycle, WE goes Low after LCAS/UCAS
; thus, input data is strobed by WE and all setup/hold times are referenced to the falling edge of WE. Since this
device is an I/O common type, when the delayed write or read-modified-write is executed, I/O data have to be
controlled by OE.
DATA OUTPUT
The three-state buffers are LVTTL compatible with a fanout of one TTL load. Polarity of the output data is identical
to that of the input; the output buffers remain in the high-impedance state until the column address strobe goes
Low. When a read or read-modify-write cycle is executed, valid outputs are obtained under the following conditions:
t
RAC
:
from the falling edge of RAS when t
RCD
(max.) is satisfied.
t
CAC
:
from the falling edge of LCAS (for DQ
1
-DQ
8
) UCAS (for DQ
9
-DQ
16
) when t
RCD
is greater than t
RCD
(max.).
t
AA
:
from column address input when t
RAD
is greater than t
RAD
(max.).
t
OEA
:
from the falling edge of OE when OE is brought Low after t
RAC
, t
CAC
, or t
AA
.
The data remains valid until either LCAS/UCAS or OE returns to a High logic level. When an early write is executed,
the output buffers remain in a high-impedance state during the entire cycle.
Parameter
Notes
Symbol
Min.
Typ.
Max.
Unit
Ambient
Operating Temp
Supply Voltage
V
CC
3.0
3.3
3.6
V
0
°
C to +70
°
C
V
SS
0
0
0
Input High Voltage, all inputs
V
IH
2.0
—
V
CC
+0.3
V
Input Low Voltage, all inputs(*)
V
IL
–0.3
—
0.8
V
Input Low Voltage, DQ(*)
V
ILD
–0.3
—
0.8
V
1
1
1
1