© 1999 Fairchild Semiconductor Corporation DS009964 www.fairchildsemi.com
November 1988
Revised November 1999
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• 74ACT521 8-Bi
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ator
74AC521 74ACT521
8-Bit Identity Comparator
General Description
The AC/ACT521 is an expandable 8-bit comparator. It
compares two words of up to eight bits each and provides a
LOW output when the two words match bit for bit. The
expansion input I
A = B
also serves as an active LOW enable
input.
Features
a73 I
CC
reduced by 50%
a73 Compares two 8-bit words in 6.5 ns typ
a73 Expandable to any word length
a73 20-pin package
a73 Outputs source/sink 24 mA
a73 ACT521 has TTL-compatible inputs

Ordering Code:
Device also available in Tape and Reel. Specify by appending suffix letter “X” to the ordering table.
Logic Symbols
IEEE/IEC
Connection Diagram
Pin Descriptions
FACT is a trademark of Fairchild Semiconductor Corporation.
Order Number Package Number Package Description
74AC521SC M20B 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300” Wide Body
74AC521SJ M20D 20-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
74AC521PC N20A 20-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide
74ACT521SC M20B 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300” Wide Body
74ACT521SJ M20D 20-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
74ACT521PC N20A 20-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide
Pin Names Description
A
0
–A
7
Word A Inputs
B
0
–B
7
Word B Inputs
T
A = B
Expansion or Enable Input
O
A = B
Identity Output