Has anyone used the 74c922 16-key encoder chip? am just wondering whether you have experianced the same problems as i am!?

When i connect the data output pin via an inverter to the output enable pin, i will get what appears to be undebounced signals when i press a button although it says the debouncing is taken care of via a capacitor..

I cure this problem by connecting the output enable pin directly to ground but then when i press the a key the outputs latch! i don't want the outputs to latch, i am just wondering if anyone has come across the same/similar problem?

 

Do you mean data available pin?

 

yeah i connect the data available pin via the inverter back to the output enable pin...

when i do this, before i push a button the data available pin is low therefore the output enable pin is held high and all outputs are low. However when i push a button on the key pad the data available pin goes high therefore the ouput enable pin goes low; which it does.

The problem seems to be when i release the button there are small spikes on each of the output lines! I have no idea what is causing these, these small spikes are being interpreted by the rest of the logic chips as logic '1's.

To cure this i connect the output enable pin directly to ground but then the outputs latch! which i do not want....

I also noticed that if i tie the output enable pin directly to +Vcc i.e. disable the outputs i still get these voltage spikes from the outputs when i press a button on the keypad!

Do you think there is possiblly a flaw with the chip or possible broken?!

 

The output enable is a tri-state control, meaning it forces the outputs to high impedance when it is at VCC. The logic levels are undefined in this state, and noise will easily show up as a result of key presses. If you are sending this data to another CMOS device, you can solve the problem by adding a 10kohm pulldown from each data output to GND. This will guarantee a logic "0" state when the outputs are disabled.