The data output functions may be enabled or disabled by various signals at the OE and DIR inputs. Data input functions are always enabled;
i.e., data at the bus pins will be stored on every LOW-to-HIGH transition of the appropriate clock inputs.
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2
74LCX646
Functional Description
In the transceiver mode, data present at the HIGH imped-
ance port may be stored in either the A or B register or
both. The select (SAB, SBA) controls can multiplex stored
and real-time. The examples shown below demonstrate the
four fundamental bus-management functions that can be
performed.
The direction control (DIR) determines which bus will
receive data when OE is LOW. In the isolation mode (OE
HIGH), A data may be stored in one register and/or B data
may be stored in the other register. When an output func-
tion is disabled, the input function is still enabled and may
be used to store and transmit data. Only one of the two
busses, A or B, may be driven at a time.
Real-Time Transfer
Bus B to Bus A
Real-Time Transfer
Bus A to Bus B
OE DIR CPAB CPBA SAB SBA
L
L
X
X
X
L
OE
L
DIR
H
CPAB CPBA
X
X
SAB
L
SBA
X
Transfer Storage
Data to A or B
Storage
OE
L
L
DIR
L
H
CPAB CPBA
X
H or L
H or L
X
SAB
X
H
SBA
H
X
OE
L
L
H
H
DIR
H
L
X
X
CPAB CPBA
X
X
X
X
SAB
L
X
X
X
SBA
X
L
X
X
3
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74LCX646
Logic Diagram
Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.
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4
74LCX646
Absolute Maximum Ratings
(Note 3)
Symbol
V
CC
V
I
V
O
I
IK
I
OK
I
O
I
CC
I
GND
T
STG
Parameter
Supply Voltage
DC Input Voltage
DC Output Voltage
DC Input Diode Current
DC Output Diode Current
DC Output Source/Sink Current
DC Supply Current per Supply Pin
DC Ground Current per Ground Pin
Storage Temperature
Value
Conditions
Units
V
V
Output in 3-STATE
Output in HIGH or LOW State (Note 4)
V
I
<
GND
V
O
<
GND
V
O
>
V
CC
V
mA
mA
mA
mA
mA
−
0.5 to
+
7.0
−
0.5 to
+
7.0
−
0.5 to
+
7.0
−
0.5 to V
CC
+
0.5
−
50
−
50
+
50
±
50
±
100
±
100
−
65 to
+
150
°
C
Recommended Operating Conditions
(Note 5)
Symbol
V
CC
V
I
V
O
I
OH
/I
OL
Supply Voltage
Input Voltage
Output Voltage
Output Current
HIGH or LOW State
3-STATE
V
CC
=
3.0V
−
3.6V
V
CC
=
2.7V
−
3.0V
V
CC
=
2.3V
−
2.7V
T
A
Free-Air Operating Temperature
Input Edge Rate, V
IN
=
0.8V
−
2.0V, V
CC
=
3.0V
Parameter
Operating
Data Retention
Min
2.0
1.5
0
0
0
Max
3.6
3.6
5.5
V
CC
5.5
Units
V
V
V
±
24
±
12
±
8
−
40
0
85
10
mA
°
C
ns/V
∆
t/
∆
V
Note 3:
The Absolute Maximum Ratings are those values beyond which the safety of the device cannot be guaranteed. The device should not be operated
at these limits. The parametric values defined in the Electrical Characteristics tables are not guaranteed at the Absolute Maximum Ratings. The “Recom-
mended Operating Conditions” table will define the conditions for actual device operation.
Note 4:
I
O
Absolute Maximum Rating must be observed.
Note 5:
Unused inputs or I/Os must be held HIGH or LOW. They may not float.
Microchip MCU
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