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74C922-SO IC
Keyboard / Keypad Encoder for up to 16 switches
MM74C922 Replacement ICGeneral Description
The 74C922-SO is designed as a replacement chip for the obsolete MM74C922 surface mountpart. The 74C922-SO contains all the logic necessary to encode a SPST keyboard switch array
up to 4 by 4 in size and provide a 4 bit parallel output and a data available signal. The data
available signal goes high when a key is pressed, and goes low before another key output isgenerated. The data output pins keep their state even after the key is released. The array canbe a 4 x 4 array, but smaller arrays such as a 3 x 4 array or any smaller size can be used. The74C922-SO handles debouncing of the keys as well. No external capacitors are required fortiming; all timing is internally generated. No external diodes are required in the array to prevent
key ghosting in a two key rollover situation. A .1 uF bypass capacitor is suggested across theVDD and VSS pins. The part uses the standard 20 pin .3 inch width SOIC package.

Features• Replacement Chip for MM74C922• Fully encodes a key switch array. (up to 4 x 4)
• No external parts required.
• Low power consumption 1.5 mA typical.
• Supply voltage 2.4 to 5.25 volts.
• Last key pressed retained on data outputs.
• All timing internally generated.
• 2 Key rollover.
• On chip row input resistors.
• Internal key bounce elimination.
• TTL and CMOS compatible outputs.
• Part is in full production.
• SOIC 20 Pin Package.

Part Number 74C922-SO
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Example Circuit
2.4 - 5 V
74C922-SO
12345678910ROWY1VDD
ROWY2 DATAOUTAROWY3 DATAOUTBROWY4 DATAOUTCNCDATAOUTD
NC
NCNC
NC
COLX4 DATAAVAIL
COLX3COLX1VSSCOLX220191817161514131211DATA OUT A
DATA OUT BDATA OUT CDATA OUT DDATA AVAILABLE

KEYBOARD

Connection Diagram
74C922-SO
12345678910ROWY1VDD
ROWY2 DATAOUTAROWY3 DATAOUTBROWY4 DATAOUTCNCDATAOUTDNCNCNCNC
COLX4 DATAAVAIL
COLX3COLX1VSSCOLX220191817161514131211Pin Description
Pin #12345678910

Description
Row Y1Row Y2Row Y3Row Y4NCNC
NCCol X4
Col X3
VSSPin #20191817161514131221

Description
VDD
Data Out A
Data Out B
Data Out C
Data Out DNC
NCData Avail
Col X1Col X2Col X1 – Col X4These pins are open drain column driver outputs to the key matrix.
Row Y1 – Row Y4
These pins are the row inputs from the key matrix. These inputs have 5.6K (nominal) pull up
resistors on chip.
Data Out A – Data Out D
These pins are the encoded data output. The output keeps the state of the last key pressed evenafter the key is released. These pins are TTL and CMOS compatible.

Part Number 74C922-SO
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Data Avail
This pin goes high when a key is pressed, and low when a key is released. This pin goes low in a
two key rollover situation before returning high. This pin is TTL and CMOS compatible.
VSS
Connect to system ground.
VDD
Connect to supply voltage of 2.4 to 5 volts. A .1 uF decoupling capacitor to ground isrecommended.

NOTES:
No connection is required to the NC pins. If external capacitors are used on pins 6 and 7 fromyour previous design, they do not need to be removed. If pin 14 is grounded on your previous
design, it does not need to be changed. Pins 5 and 15 must be left unconnected.

Truth Table
ROWY1
ROWY1
ROWY1
ROWY1
ROWY2
ROWY2
ROWY2
ROWY2
ROWY3
ROWY3
ROWY3
ROWY3
ROWY4
ROWY4
ROWY4
ROWY4COLX1X

COLX2COLX3COLX4X
X
XX
X
X
XX
X
X
X
XXXX

DATAOUTD
0000000011111111

DATAOUTC
0000111100001111

DATAOUTB
0011001100110011

DATAOUTA
010
1010101010101

Absolute Maximum Ratings
SymbolDescription

Min

TypicalMax

Units

Tstg
Ta
V dd
V io
Imio
ESD

Storage Temperature
Operating Temperature-55-40-0.5

25+100+85+6.0ºCºC
VVmAV

LU

Latch up current

V dd - V ss Voltage
Input Voltage
Maximum current into any pin
Electrostatic Discharge Voltage

Vss - 0.5-25
2000

V dd +0.5+50200

Part Number 74C922-SO
December 2012 Page 3 of 5mANotes

Human Body ModelESD

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DC Electrical Characteristics
SymbolDescription

Min

V ddIdd
V oh
V ol
V ih
V il
Ioh
Iol
Cio
Iil
Rpu

Supply Voltage
Supply Current
High Output Level
Low Output Voltage
Input High Level
Input Low Level
High Level Source Current
Low Level Sink Current
Capacitive load
Input leakage
Pull Up Resistors On Row Inputs

2.4

TypicalMax

Units

1.55.258VmAVVVVmA
mApF
nAk?

V dd - 1.00.75
2.14

3.5
1
5.6

0.8
1025
108Notes
V dd = 5V
Ioh=10 mA
Iol=25 mA

Differences between the MM74C922 and 74C922-SO
Power Supply
The MM74C922 part is capable of a supply voltage of 3 to 15 volts. The 74C922-SO has a more
limited power supply of 2.4 to 5.25 volts.
Timing Capacitors
The MM74C922 part requires timing capacitors on pins 6 and 7. The 74C922-SO generates all
timing internally, and these capacitors are not required. These pins are no connects on the74C922-SO. If capacitors are present on your design, they do not need to be removed.
Tristate Outputs
The DataOut pins of the MM74C922 are tristate outputs controlled by pin 14 –OutputEnable. The
DataOut pins of the 74C922-SO are not tristate. Pin 14 is a no connect, and may be grounded orleft open. If your design needs tristate outputs, consult the factory for solutions.
Timing
The timing of the 74C922-SO is more relaxed. The data setup to Data Avail timing is longer, andthe low output time in a two key roll over situation is improved.

Theory Of Operation
The 74C922-SO is a custom programmed microprocessor designed to emulate the MM74C922.
The open drain COLX pins are pulsed low one at a time, and the ROWY pins are sampled tocheck for key switch closures. If a key is detected, scanning stops until the key is released. The
pressed key is encoded and placed on the DataOut pins, and the DataAvail output is set low until
the key is released. When the key is released, the DataAvail output is set hi again and scanning
continues.

Part Number 74C922-SO
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Physical Dimensions

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Part Number 74C922-SO
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