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74C922 Datasheet(PDF) 1 Page - Fairchild Semiconductor |
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74C922 Datasheet(HTML) 1 Page - Fairchild Semiconductor |
1 / 10 page October 1987 Revised January 1999 © 1999 Fairchild Semiconductor Corporation DS006037.prf www.fairchildsemi.com 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 k Ω 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 s 50 k Ω 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: 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 |
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