Okay, my logics are being...illogical.

gtr_stitch

New Member

• Mar 14, 2011

• #1

Alright, so...I have like, a few logic ic chips and none of them work right at all. I have a 4077, 4093 and m74hc03b1r (quad nand) and each one, quite "reliably", doesn't seem to respond. Is there any special instructions? Do the inputs require a certain signal or something? I am just...disappointed. So many things I could do with logic...if I could just get the darn things to work. Any ideas?

I use an led on the output and it lights up at first (or doesn't...depending on the logic) but when any of the inputs go high, either nothing happens or whatever does happen doesn't follow the truth table for that particular logic. This is highly aggravating.

 

ronv

Well-Known Member

Most Helpful Member

• Mar 14, 2011

• #2

Make sure you don't have any floating inputs. Tie any unused inputs either high or low to satisy your truth table.

 

gtr_stitch

New Member

• Mar 14, 2011

• #3

Oh really? Dang I didn't even consider that. That has to be done on this counter that I have. Any unused out puts need to be tied to low in order for proper operation.

 

MikeMl

Well-Known Member

Most Helpful Member

• Mar 14, 2011

• #4

No, you never tie outputs to anything but another inputs. INPUTs that are not driven from outputs of other chips have to be tied low or high depending on what that particular input does. Tying high or low might be a connection to chip Vss or Chip Vdd, or for some logic families, you may need a resistor network.

 

gtr_stitch

New Member

• Mar 14, 2011

• #5

Is this the case with a 4024? I actually read in the datasheet that any output you're not using should be tied to ground, and it actually seemed to do the trick (until of course I got more LEDs. Then I didn't have any unused outputs)

 

gtr_stitch

New Member

• Mar 14, 2011

• #6

RonV...thanks a ton! It didn't even dawn on me that when it comes to logic, there us a high and a low...so duh, can't really leave one floating when you need a high or a low. Thanks again!

 

ronv

Well-Known Member

Most Helpful Member

• Mar 14, 2011

• #7

Glad it helped.

 

MikeMl

Well-Known Member

Most Helpful Member

• Mar 14, 2011

• #8

The 4024 has only two logic inputs: CLOCK~ and RESET. Assuming you are driving CLOCK, but not using RESET, you need to tie it to ground. Unused outputs: Q1-7 leave them open.

 

audioguru

Well-Known Member

Most Helpful Member

• Mar 14, 2011

• #9

gtr_stitch said:

I actually read in the datasheet that any output you're not using should be tied to ground

Click to expand...

Absolutely not! Read the datasheet again.
You never ever connect an output to ground! It will smoke if it tries to go high.
Inputs can be connected to ground if you want them to be low.

 

gtr_stitch

New Member

• Mar 14, 2011

• #10

you're absolutely right. i'm not sure where i read it, but i skimmed through the datasheet again and it wasn't in there. [inserts foot in mouth]
i am positive i read it somewhere, but (as per the crappy schematic i referenced to once before) i suppose i should first consult the experts, which is why i am always glad to see when any of you post on my inquiries
luckily for me, though, the 4024 survived when i did what i wasn't supposed to do!
as for the logic...i wasn't using my own logic. if i wanted the input low...i should tie it low (duh!)

 

D

Diver300

Well-Known Member

Most Helpful Member

• Mar 15, 2011

• #11

audioguru said:

You never ever connect an output to ground! It will smoke if it tries to go high.

Click to expand...

I agree that outputs should never be connected to ground. However, 74HC circuits limit at about 25 mA. (HEF4000 series limit at lower currents). That will get the ICs warm, but they probably won't be destroyed if shorted to ground.

Other ICs will smoke very quickly if shorted.