Matrix MS001 Manuel d'utilisateur télécharger pdf

October 1987

Revised January 1999

MM74C922 • MM74C923 16-Key Encoder • 20-Key Encoder

MM74C922 • MM74C923

16-Key Encoder • 20-Key Encoder

General Description

The MM74C922 and MM74C923 CMOS key encoders pro-

vide all the necessary logic to fully encode an array of

SPST switches. The keyboard scan can be implemented

by either an external clock or external capacitor. These

encoders also have on-chip pull-up devices which permit

switches with up to 50 kΩ on resistance to be used. No

diodes in the switch array are needed to eliminate ghost

switches. The internal debounce circuit needs only a single

external capacitor and can be defeated by omitting the

capacitor. A Data Available output goes to a high level

when a valid keyboard entry has been made. The Data

Available output returns to a low level when the entered

key is released, even if another key is depressed. The Data

Available will return high to indicate acceptance of the new

key after a normal debounce period; this two-key roll-over

is provided between any two switches.

An internal register remembers the last key pressed even

after the key is released. The 3-STATE outputs provide for

easy expansion and bus operation and are LPTTL compat-

ible.

Features

■ 50 kΩ maximum switch on resistance

■ On or off chip clock

■ On-chip row pull-up devices

■ 2 key roll-over

■ Keybounce elimination with single capacitor

■ Last key register at outputs

■ 3-STATE output LPTTL compatible

■ Wide supply range: 3V to 15V

■ Low power consumption

Ordering Code:

Device also available in Tape and Reel. Specify by appending suffix letter “X” to the ordering code.

Connection Diagrams

Pin Assignment for DIP

Top View

MM94C922

Pin Assignment for SOIC

Top View

MM74C922

Order Number Package Number Package Description

MM74C922N N18A 18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide

MM74C922WM M20B 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300” Wide

MM74C923WM M20B 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300” Wide

MM74C923N N20A 20-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide

1 2 3 4 5 6 7 8 9 10

Résumé du contenu

Page 1 - MM74C922 • MM74C923

Page 2 - Truth Tables

Fairchild does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and Fairchild reserves the rig

Page 3 - Block Diagram

www.fairchildsemi.com 2MM74C922 • MM74C923Connection Diagrams (Continued)Pin Assignment forDIP and SOIC PackageTop ViewMM74C923Truth Tables(Pins 0 th

Page 4

3 www.fairchildsemi.comMM74C922 • MM74C923 Block Diagram

Page 5

www.fairchildsemi.com 4MM74C922 • MM74C923Absolute Maximum Ratings(Note 2)Note 2: “Absolute Maximum Ratings” are those values beyond which thesafety o

Page 6 - Switching Time Waveforms

5 www.fairchildsemi.comMM74C922 • MM74C923 DC Electrical Characteristics (Continued)AC Electrical Characteristics (Note 3)TA = 25°C, CL = 50 pF, un

Page 7 - Typical Applications

www.fairchildsemi.com 6MM74C922 • MM74C923Switching Time WaveformsT1 ≈ T2 ≈ RC, T3 ≈ 0.7 RC, where R ≈ 10k and C is external capacitor at KBM input.FI

Page 8 - Theory of Operation

7 www.fairchildsemi.comMM74C922 • MM74C923 Typical Performance Characteristics Typical Irp vs VIN at Any Y Input Typical Ron vs VOUT at Any X Output T

Page 9

www.fairchildsemi.com 8MM74C922 • MM74C923Asynchronous Data Entry Onto Bus (MM74C922)Outputs are in 3-STATE until key is pressed, then data is placed

Page 10

9 www.fairchildsemi.comMM74C922 • MM74C923 Physical Dimensions inches (millimeters) unless otherwise noted18-Lead Plastic Dual-In-Line Package (PDIP),

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Matrix MS001 Manuel d'utilisateur

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Résumé du contenu

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