About 74C922( Keypad encoder)

[kyutekyute101]

Hi
How come the data from the keypad encoder's output is lower voltage that its data sheet... ( when 5V Vcc is applied ). Do i need a pull up resistor to bring up the voltage ??? i REALLY cant find the solution for it....

Pls reply me.
Thanks

 

[Nigel Goodwin]

Hi
How come the data from the keypad encoder's output is lower voltage that its data sheet... ( when 5V Vcc is applied ). Do i need a pull up resistor to bring up the voltage ??? i REALLY cant find the solution for it....

How low is it?, and how are you measuring it?.

 

[G8RPI]

Hi,
The 74c922 is compatable with both CMOS and low power TTL. The output voltage "high" when connected to CMOS (assuming 5V supply) is specified as 4.5V minimum. However when connected to TTL, it is only specified as 2.4V minimum. If you are connected to TTL and the high voltage is above 2.4V the IC is within specification.
The only other possible problem is that you are not pulling the output enable input (pin 13) low and noise is causing a PWM like modulation of the output. This problem would be obvious with a 'scope but not a voltmeter.

G8RPI.