HIT HD74HC679 Datasheet
HD74HC679
12-bit Address Comparator
Description
The HD74HC679 address comparator simplifies addressing of memory boards and/or other peripheral
devices. The four P inputs are normally hard wired with a preprogrammed address. An internal decoder
determines what input information applied to the 12 A inputs must be low or high to cause a low state at the
output (Y). For example, a positive-logic bit combination of 0111 (decimal 7) at the P input determines
that inputs A1 through A7 must be low and that inputs A8 through A12 must be high to cause the output to go
low. Equality of the address amplified at the A inputs to the preprogrammed address is indicated by the
output being low.
The HD74HC679 features and enable input (G). When G is low, the device is enabled. When G is high,
the device is disabled and the output is high regardless of the A and P inputs.
Features
• High Speed Operation: tpd (A to Y) = 18 ns typ (CL = 50 pF)
• High Output Current: Fanout of 10 LSTTL Loads
• Wide Operating Voltage: VCC = 2 to 6 V
• Low Input Current: 1 µA max
• Low Quiescent Supply Current: ICC (static) = 4 µA max (Ta = 25°C)
HD74HC679
Function Table
Inputs
G P
3P2P1P0A1A2A3A4A5A6A7A8A9A10A11A12
L LL LLHHHHHHHHHHHH L
L LL LHLHHHHHHHHHHH L
L LL HLLL HHHHHHHHHH L
L LL HHLL LHHHHHHHHH L
L LHLLLLLLHHHHHHHH L
L LHLHLLLLLHHHHHHH L
L LHHLLLLLLLHHHHHH L
L LHHHLLLLLLLHHHHH L
L HLLLLLLLLLLLHHHH L
L HLLHLLLLLLLLLHHH L
L HLHLLLLLLLLLLLHH L
L HLHHLLLLLLLLLLLH L
L HHLLLLLLLLLLLLLL L
L HHLHXXXXXXXXXXXX H
L HHHLXXXXXXXXXXXX H
L HHHHLLLLLLLLLLLL L
L All other combinations H
H Any combination H
Output Y
2
Pin Arrangement
HD74HC679
A
A
A
A
A
A
A
A
A
GND
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
20
19
18
17
16
15
14
13
12
11
V
CC
G
Y
P
3
P
2
P
1
P
0
A
12
A
11
A
10
(Top view)
3
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