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DIY Stompboxes => Digital & DSP => Topic started by: served on December 18, 2010, 05:38:12 AM

Title: 74C373 Octal Latch problem
Post by: served on December 18, 2010, 05:38:12 AM
Hi.

I am having some problems with 74C373 Octal Latch.
If I power it up. All the outputs are "On". If I feed one D with signal (+5V) then Q will rise and the others fall. But If I stop feeding D everything falls.

What am I doing wrong? Why are Q-s on if I power it up? Why Q falls to 0 if I stop giving input.

I would like Qx to stay high, if I momentarily give signal to Dx.
If I give signal to Dx+n then Qx should go low and Qx+n should go high.

And I dont like the start up thing.
I hope its not too comlicated, but I don't know how to explain.

Octal latch is MM74C373N


A.
Title: Re: 74C373 Octal Latch problem
Post by: served on December 18, 2010, 05:54:25 AM
OK. I got it working. I needed that pulldown resistor for LE.

But still. Why are all Qs High, If I power it up?

A.
Title: Re: 74C373 Octal Latch problem
Post by: PRR on December 18, 2010, 07:09:41 PM
http://www.geofex.com/Article_Folders/VCA%20Applications.pdf   - page 5.

Don Lancaster's TTL Cookbook, also CMOS Cookbook.

Generally: all unused pins MUST be forced high or low, the start-up state of a flip-flop is NOT defined (unless it has a Reset pin and you use it tight).