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參數(shù)資料
| 型號： | MM54C923 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 20-Key Encoder(20鍵編碼器) |
| 中文描述： | 20鍵編碼器（20鍵編碼器） |
| 文件頁數(shù)： | 1/10頁 |
| 文件大?。?/td> | 218K |
| 代理商： | MM54C923 |
TL/F/6037
M
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 k
X
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
é
outputs provide
for easy expansion and bus operation and are LPTTL com-
patible.
Features
Y
50 k
X
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
3V to 15V
Y
Low power consumption
Connection Diagrams
Pin Assignment for
Dual-In-Line Package
TL/F/6037–1
Top View
Order Number MM54C922 or
MM74C922
Pin Assignment
for SOIC
TL/F/6037–14
Top View
Order Number MM74C922
Pin Assignment for
DIP and SOIC Package
TL/F/6037–2
Top View
Order Number MM54C923 or
MM74C923
TRI-STATE
é
is a registered trademark of National Semiconductor Corporation.
C
1995 National Semiconductor Corporation
RRD-B30M105/Printed in U. S. A.
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