74F85 Datasheet, PDF (4/10 Pages) NXP Semiconductors – 4-bit magnitude comparator

Philips Semiconductors
4-bit magnitude comparator
Product specification
74F85
APPLICATION
INPUTS
(LSB) B23
B3
A23
A3
B22
B2
A22
A2
B21
B1 A<B
A21
A1 A=B
NC
B20
B0 A>B
A20
A0
B19
L
A19
I_A<B
I_A=B
I_A>B
B18
B3
A18
A3
B17
B2
A17
A2
B16
B1 A<B
A16
A1 A=B
NC
B15
B0 A>B
A15
A0
B14
L
A14
I_A<B
I_A=B
I_A>B
B13
B3
A13
A3
B12
B2
A12
A2
B11
B1 A<B
A11
A1 A=B
NC
B10
B0 A>B
A10
A0
B9
L
A9
I_A<B
I_A=B
I_A>B
B3
A3
B2
A2
B1 A<B
A1 A=B
B0 A>B
A0
A<B
A=B
A>B
OUTPUTS
B8
B3
A8
A3
B7
B2
A7
A2
B6
B1 A<B
A6
A1 A=B
NC
B5
B0 A>B
A5
A0
B4
L
A4
I_A<B
I_A=B
I_A>B
(LSB)
B3
A3
B2
A2
B1
A1
B0
A0
L
H
L
B3
A3
B2
A2
B1 A<B
A1 A=B
B0 A>B
A0
I_A<B
I_A=B
I_A>B
SF00079
Figure 1. Comparison of Two 24-Bit Words
The parallel expansion scheme shown in Figure 1 demonstrates the
most efficient general use of these comparators. The expansion
inputs can be used as a fifth input bit position except on the least
significant device, which must be connected as in the serial scheme.
The expansion inputs used by labeling I_A>B as an “A” input, I_A<B as
a “B” input and setting I_A=B = Low. The 74F85 can be used as a 5-bit
comparator only when the outputs are used to drive the (A0–A3) and
(B0–B3) inputs of another 74F85 device. The parallel technique can
be expanded to any number of bits as shown in Table 1.
Table 1.
WORD LENGTH
1–4 bits
5–24 bits
25–120 bits
NUMBER OF
PACKAGES
1
2–6
8–31
TYPICAL SPEEDS
74F
12ns
22ns
34ns
September 27, 1994
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