Hi.
What to do with the unused inputs on a 4070 XOR, a LM339N comparators, a AM26LS31C differential line driver sender and a AM26LS31 differential line driver receiver ?
Should the inputs be connected to ground ? Or should it go via a resistor to ground ?
Or should the + input go to +V and the - input to ground ?
Or what ? :-)
-- vroemm wanadoo nl
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They should be 'tied' in such condition that they DON'T respond to noise. Open cirquit is 'no, no' so either ground (direct) or bus through resistor. In every multi-input device this signal should create a "don't care" condition so other inputs can perform their respective functions.
HTH
Stanislaw Slack user from Ulladulla.
So for the 4070 you tie both inputs to ground or VCC (doesn't matter), but for the comparators and differential line receiver you tie the inputs so that there's a healthy difference (I _think_ you can get away with one to ground and one to VCC, but you'll have to check your particular part's common mode input range).
For any of them, if you tie them to the rail through a resistor you leave that gate as an easy-to-hack resource in case you need it later -- tying a pin directly to ground or VCC means lifting the pin and soldering a flying lead if you want to use it later.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
You're talking about four different parts and three different technologies, so one would expect different termination methods for unused inputs. For those parts susceptible to oscillation due to internal feedback, you want a low impedance termination. This means the '339, '31, and '33 or '32 parts. For the '339 take one input to GND and the other to Vcc, makes no matter which one, and do the same for '33 and '32 differential line receiver. The '31 driver has only one signal input per gate, tie it to GND or VCC, makes no difference. For 4000 series logic, terminate unused inputs to any of GND or VCC, in any combination , makes no difference.
Tie them high or low as convenient. No resistors should be required.
Graham
This is NOT logic, just experience which arrives in time.
Have fun.
Stanislaw.
combination
Realy? If memory serves it responds to low input, so you cannot use ground on unused inputs as you force output in certain state. You are right on segments that have no part in the overall connectivity but we were addressing "unused inputs".
Cheers
Stanislaw.
In the case of the original question the unused inputs have also unused outputs. Not connected at all.
-- vroemm wanadoo nl
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