MM74C922 • MM74C923 16-Key Encoder • 20-Key Encoder
October 1987
Revised January 1999
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
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
MM74C922N
MM74C922WM
MM74C923WM
MM74C923N
Package Number
N18A
M20B
M20B
N20A
Package Description
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 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 suffix letter “X” to the ordering code.
Connection Diagrams
Pin Assignment for DIP
Pin Assignment for SOIC
Top View
MM74C922
Top View
MM94C922
© 1999 Fairchild Semiconductor Corporation
DS006037.prf
www.fairchildsemi.com
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
