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PDF 74C923 Data sheet ( Hoja de datos )
| Número de pieza | 74C923 | |
| Descripción | 16/ 20-Key Encoder | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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July 1993
MM54C922 MM74C922 16-Key Encoder
MM54C923 MM74C923 20-Key Encoder
General Description
These 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 have on-chip pull-
up devices which permit switches with up to 50 kX on resist-
ance 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 en-
tered 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 TRI-STATE outputs provide
for easy expansion and bus operation and are LPTTL com-
patible
Features
Y 50 kX maximum switch on resistance
Y On or off chip clock
Y On-chip row pull-up devices
Y 2 key roll-over
Y Keybounce elimination with single capacitor
Y Last key register at outputs
Y TRI-STATE outpust LPTTL compatible
Y Wide supply range
Y Low power consumption
3V to 15V
Connection Diagrams
Pin Assignment for
Dual-In-Line Package
Pin Assignment
for SOIC
Pin Assignment for
DIP and SOIC Package
Top View
TL F 6037–1
Order Number MM54C922 or
MM74C922
TL F 6037 – 14
Top View
Order Number MM74C922
Top View
TL F 6037 – 2
Order Number MM54C923 or
MM74C923
TRI-STATE is a registered trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation TL F 6037
RRD-B30M105 Printed in U S A
1 page  
Typical Performance Characteristics
Typical Irp vs VIN at
Any Y Input
Typical Ron vs VOUT at
Any X Output
TL F 6037 – 6
Typical FSCAN vs COSC
TL F 6037 – 7
Typical Debounce Period
vs CKBM
TL F 6037 – 8
Typical Applications
Synchronous Handshake (MM74C922)
TL F 6037 – 9
Synchronous Data Entry Onto Bus (MM74C922)
TL F 6037 – 10
TL F 6037 – 11
Outputs are enabled when valid entry is made and
go into TRI-STATE when key is released
Note 3 The keyboard may be synchronously scanned by omitting the capacitor at osc and driving osc directly if the system clock rate is lower than 10 kHz
5
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet 74C923.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| 74C922 | 16-Key Encoder 20-Key Encoder |  Fairchild Semiconductor |
| 74C922 | 16/ 20-Key Encoder | National Semiconductor |
| 74C923 | 16-Key Encoder 20-Key Encoder | Fairchild Semiconductor |
| 74C923 | 16/ 20-Key Encoder | National Semiconductor |
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