Logic Analyzer output of 7445N BCD-to-Decimal

[Arnie_8446]

Hello All,

I am testing the output of a 7445N BCD-to-Decimal decoder with the use of Multisim 10 word generator and the logic analyzer.  I have the inputs of the 7445N connected to the word generator counting up from 0 to 9 binary.  The first four inputs of the logic analyzer are connected to the inputs of the 7445N as well.  I can see the correct pattern of binary number being generated by the word generator at the logic analyzer. However, the logic analyzer connections to the output of the 7445N shows flat lines.  I don't see the binary numbers generated.  I connected logic probes to the output of the 7445N, and a binary pattern is shown.  If I connect a single line from the logic analyzer to the output of the 7445N, then I can see the logic low and high for that particular pin.  But again, if I connect more than one line from the logic analyzer to the 7445N, it goes back to a flat line.  Has anyone seen this before?  Is there a specific method to test this particular IC output with the logic analyzer?   Any help would be greatly appreciated!

Thanks,
Arnie

[lacy]

On the outputs of the 7445N you need to tie in pull up resistors to VCC. Ther outputs are active low and therefore must remain high until switched low.

If you need me to post a schematic I can. Just let me know.

Hope this helps

[Arnie_8446]

Hi Lacy,

Could you please post a diagram?  I tried it with a 470 ohm resistor tied to a 5 V Vcc, but I got the same result. 

Thanks for your help!
Arnie

[lacy]

I will do you even better. I will post the complete MS10 file for you to look at. All the settings of the simulator are defaulted. I thought I would let you know that so you wouldn't think I fiddled with the settings to make it work.

Here it is and I hope this helps:

[Arnie_8446]

Hi Lacy,

This is good!  I really appreciate your help with this.

Thank You!
Arnie