LTspice: 'AND' device oddity. Is this a bug?

I've just noticed that the AND device in the 'Digital' folder behaves oddly. A '1' and a '0' as inputs should provide a '0' output, but do so only if some resistance is included in the '0' input !!??

What's going on?
Is this a bug or a 'feature', given that the 'A' devices are apparentlyproprietary?

alec_t said:

I've just noticed that the AND device in the 'Digital' folder behaves oddly. A '1' and a '0' as inputs should provide a '0' output, but do so only if some resistance is included in the '0' input !!??
View attachment 113404
What's going on?
Is this a bug or a 'feature', given that the 'A' devices are apparentlyproprietary?

Click to expand...

Hi Alex..

Heh...yes...confusing...but not a bug. This one fools a lot of users. Including me when I first started using LTspice

The AND gate is used for many different types of AND functions, like an NAND gate for example.
When an input is connected directly to ground (like with an LTspice ground symbol), LTspice treats it as an unused pin and eliminates the pin from the circuit. So its basically ignored. Unused pins should be left unconnected. If you need in input to be active, pull it high, or low (with a resistor), or connect it to another component. The A devices aren't really intended to be used in their bare form, but to be encapsulated with other devices to form a complete logic function.

Some of this is described in the LTspice Help.

Hope that helps...

eT

Thanks for the helpful info. Now that you mention it I do recall reading about the 'ignore pin' feature. It may partly explain the CD4013 model not following the datasheet when both the Set and Reset pins are pulled high?

alec_t said:

Thanks for the helpful info. Now that you mention it I do recall reading about the 'ignore pin' feature. It may partly explain the CD4013 model not following the datasheet when both the Set and Reset pins are pulled high?

Click to expand...

Hi

No...I actually discovered and reported that CD4013B bug to the LTspice group a few years ago. They have since fixed it..so your probably using an old library.

eT

I also reported the 4013 problem a few years ago but got nowhere. The latest LTS update (a couple of weeks ago) seems to have 'un-fixed' the problem, as well as introducing arbitrary font size changes to some symbols .

Edit:
I've just re-installed the latest CD4000 model files from the Yahoo group and all seems well. The CD4013 now behaves itself and font size is restored to normal .

alec_t said:

I also reported the 4013 problem a few years ago but got nowhere. The latest LTS update (a couple of weeks ago) seems to have 'un-fixed' the problem, as well as introducing arbitrary font size changes to some symbols .

Edit:
I've just re-installed the latest CD4000 model files from the Yahoo group and all seems well. The CD4013 now behaves itself and font size is restored to normal .

Click to expand...

Hi...I checked my library file...it was fixed about 9/13/2013...

* Revision 0.64 09/13/2013 force Q=high if R AND S are high

Yes...I noticed the default font size seems to have changed in LTspice recently. Mine is showing up 0.0625 argh!

eT

eTech said:

Mine is showing up 0.0625 argh!

Click to expand...

Mine was doing that, though strangely for only some of the CD4000 symbols. I corrected a few but gave up.