Yeaaaaas asas

Páginas: 10 (2325 palabras) Publicado: 20 de marzo de 2012
MM74C922 • MM74C923 16-Key Encoder • 20-Key Encoder

October 1987 Revised April 2001

MM74C922 • MM74C923 16-Key Encoder • 20-Key Encoder
General Description
The MM74C922 and MM74C923 CMOS key encoders provide 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 haveon-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 alow 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 areLPTTL compatible.

Features
s 50 kΩ maximum switch on resistance s On or off chip clock s On-chip row pull-up devices s 2 key roll-over s Keybounce elimination with single capacitor s Last key register at outputs s 3-STATE output LPTTL compatible s Wide supply range: 3V to 15V s Low power consumption

Ordering Code:
Order Number MM74C922WM MM74C922N MM74C923WM MM74C923N Package Number M20BN18B M20B N20A Package Description 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300" Wide 18-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300" Wide 20-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300" Wide 20-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide

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

Connection Diagrams
Pin Assignment for DIP Pin Assignment for SOIC

Top View MM74C922

Top View MM74C922

© 2001 Fairchild Semiconductor Corporation

DS006037

www.fairchildsemi.com

MM74C922 • MM74C923

Connection Diagrams

(Continued) Pin Assignment for DIP and SOIC Package

Top View MM74C923

Truth Tables
(Pins 0 through 11) SwitchPosition D A T A O U T (Pins 12 through 19) Switch 12 Position D A T A O U T
Note 1: Omit for MM74C922

0

1

2

3

4

5

6

7

8 Y3, X1 0 0 0 1 0

9 Y3, X2 1 0 0 1 0

10 Y3, X3 0 1 0 1 0

11 Y3, X4 1 1 0 1 0

Y1, X1 Y1, X2 Y1, X3 Y1, X4 Y2, X1 Y2, X2 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1 1 0 0 0 0 0 1 0 0 1 0 1 0 0

Y2, X3 Y2, X4 0 1 1 0 0 1 1 1 0 0

A B C D E (Note 1)

13 Y4,X2 1 0 1 1 0

14 Y4, X3 0 1 1 1 0

15 Y4, X4 1 1 1 1 0

16

17

18

19

Y4, X1 0 0 1 1 0

Y5(Note 1), X1 Y5 (Note 1), X2 Y5 (Note 1), X3 Y5 (Note 1), X4 0 0 0 0 1 1 0 0 0 1 0 1 0 0 1 1 1 0 0 1

A B C D E (Note 1)

www.fairchildsemi.com

2

MM74C922 • MM74C923

Block Diagram

3

www.fairchildsemi.com

MM74C922 • MM74C923

Absolute Maximum Ratings(Note 2)Voltage at Any Pin Operating Temperature Range MM74C922, MM74C923 Storage Temperature Range Power Dissipation (P D) Dual-In-Line Small Outline Operating VCC Range VCC Lead Temperature (Soldering, 10 seconds) 260°C 700 mW 500 mW 3V to 15V 18V
Note 2: “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. Except for “Operating Temperature Range” they arenot meant to imply that the devices should be operated at these limits. The table of “Electrical Characteristics” provides conditions for actual device operation.

VCC − 0.3V to V CC + 0.3V

−40°C to +85°C −65°C to +150°C

DC Electrical Characteristics
Min/Max limits apply across temperature range unless otherwise specified Symbol Parameter Conditions CMOS TO CMOS VT+ Positive-Going...
Leer documento completo

Regístrate para leer el documento completo.

Estos documentos también te pueden resultar útiles

  • Yeaaaa
  • Yeaaaa
  • Yeaaaa
  • Asas
  • Asas
  • Asasa
  • Asasa
  • Asas

Conviértase en miembro formal de Buenas Tareas

INSCRÍBETE - ES GRATIS