Philips Semiconductors
Product specification
4-bit magnitude comparator
74HC/HCT85
weighted (A0 to A3 and B0 to B3), where A3 and B3 are the
most significant bits.
FEATURES
• Serial or parallel expansion without extra gating
• Magnitude comparison of any binary words
• Output capability: standard
The operation of the “85” is described in the function table,
showing all possible logic conditions. The upper part of the
table describes the normal operation under all conditions
that will occur in a single device or in a series expansion
scheme. In the upper part of the table the three outputs are
mutually exclusive. In the lower part of the table, the
outputs reflect the feed forward conditions that exist in the
parallel expansion scheme.
• ICC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT85 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
For proper compare operation the expander inputs (IA>B
IA=B and IA<B) to the least significant position must be
connected as follows: IA<B = IA>B = = LOW and
,
The 74HC/HCT85 are 4-bit magnitude comparators that
can be expanded to almost any length. They perform
comparison of two 4-bit binary, BCD or other monotonic
codes and present the three possible magnitude results at
the outputs (QA>B, QA=B and QA<B). The 4-bit inputs are
IA=B = HIGH.
For words greater than 4-bits, units can be cascaded by
connecting outputs QA<B, QA>Β and QA=B to the
corresponding inputs of the significant comparator.
QUICK REFERENCE DATA
GND = 0 V; Tamb = 25 °C; tr = tf = 6 ns
TYPICAL
SYMBOL
PARAMETER
propagation delay
CONDITIONS
UNIT
HC
HCT
tPHL/ tPLH
CL = 15 pF; VCC = 5 V
An, Bn to QA>B, QA<B
An, Bn to QA=B
20
22
ns
18
15
11
20
15
15
3.5
20
ns
ns
ns
pF
pF
I
I
A<B,, IA=B, IA>B to QA<B, QA>B
A=B to QA=B
CI
input capacitance
3.5
18
CPD
power dissipation capacitance per package
notes 1 and 2
Notes
1. CPD is used to determine the dynamic power dissipation (PD in µW):
2
PD = CPD × VCC2 × fi + ∑ (CL × VCC × fo) where:
fi = input frequency in MHz
fo = output frequency in MHz
∑ (CL × VCC2 × fo) = sum of outputs
CL = output load capacitance in pF
VCC = supply voltage in V
2. For HC the condition is VI = GND to VCC
For HCT the condition is VI = GND to VCC − 1.5 V
ORDERING INFORMATION
See “74HC/HCT/HCU/HCMOS Logic Package Information”.
December 1990
2
NXP [ NXP ]
