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PDF DM74AS646 Data sheet ( Hoja de datos )
| Número de pieza | DM74AS646 | |
| Descripción | Octal Bus Transceiver and Register | |
| Fabricantes | Fairchild Semiconductor | |
| Logotipo |  |
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October 1986
Revised March 2000
DM74AS646 • DM74AS648
Octal Bus Transceiver and Register
General Description
This device incorporates an octal bus transceiver and an
octal D-type register configured to enable multiplexed
transmission of data from bus to bus or internal register to
bus.
This bus transceiver features totem-pole 3-STATE outputs
designed specifically for driving highly-capacitive or rela-
tively low-impedance loads. The high-impedance third
state and increased high-logic-level drive provide this
device with the capability of being connected directly to and
driving the bus lines in a bus-organized system without
need for interface or pull-up components. It is particularly
attractive for implementing buffer registers, I/O ports, bidi-
rectional bus drivers, and working registers.
The registers in the DM74AS646, DM74AS648 are edge-
triggered D-type flip-flops. On the positive transition of the
clock (CAB or CBA), the input bus data is stored.
The SAB and SBA control pins are provided to select
whether real-time data or stored data is transferred. A LOW
input level selects real-time data, and a HIGH level selects
stored data. The select controls have a “make before
break” configuration to eliminate a glitch which would nor-
mally occur in a typical multiplexer during the transition
between stored and real-time data.
The enable G and direction control pins provide four modes
of operation; real-time data transfer from bus A to B, real-
time data transfer from bus B to A, real-time bus A and/or B
data transfer to internal storage, or internal store data
transfer to bus A or B.
When the enable G pin is LOW, the direction pin selects
which bus receives data. When the enable G pin is HIGH,
both buses become disabled yet their input function is still
enabled.
Features
s Switching specifications at 50 pF
s Switching specifications guaranteed over full tempera-
ture and VCC range
s Advanced oxide-isolated, ion-implanted Schottky TTL
process
s Functionally and pin-for-pin compatible with LS TTL
counterpart
s 3-STATE buffer-type outputs drive bus lines directly
Ordering Code:
Order Number Package Number
Package Description
DM74AS646WM
M24B
24-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300 Wide
DM74AS646NT
N24C
24-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-100, 0.300 Wide
DM74AS648WM
M24B
24-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300 Wide
DM74AS648NT
N24C
24-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-100, 0.300 Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
© 2000 Fairchild Semiconductor Corporation DS006324
www.fairchildsemi.com
1 page  
DM74AS646 Switching Characteristics
Symbol
Parameter
Conditions
From
(Input)
To
(Output)
Min
fMAX
tPLH
tPHL
Maximum Clock
Frequency
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
VCC = 4.5V to 5.5V,
R1 = R2 = 500Ω
CL = 50 pF
CBA or CAB
A or B
90
2
2
tPLH Propagation Delay Time
LOW-to-HIGH Level Output
tPHL Propagation Delay Time
HIGH-to-LOW Level Output
A or B
B or A
2
1
tPLH Propagation Delay Time
LOW-to-HIGH Level Output
tPHL Propagation Delay Time
HIGH-to-LOW Level Output
SBA or SAB
(Note 6)
A or B
2
2
tPZH Output Enable Time
to HIGH Level Output
2
tPZL Output Enable Time
to LOW Level Output
tPHZ Output Disable Time
from HIGH Level Output
Enable G
A or B
3
2
tPLZ Output Disable Time
from LOW Level Output
2
tPZH Output Enable Time
to HIGH Level Output
3
tPZL Output Enable Time
to LOW Level Output
tPHZ Output Disable Time
from HIGH Level Output
3
DIR A or B
2
tPLZ Output Disable Time
from LOW Level Output
2
Note 6: These parameters are measured with the internal output state of the storage register opposite to that of the bus input.
Max
8.5
9
9
7
11
9
9
14
9
9
16
18
10
10
Units
MHz
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
5 www.fairchildsemi.com
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet DM74AS646.PDF ] | |
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