I'm currently making a computer on an application called Smart Logic Simulator. However, it doesn't have any tri-state buffers and therefor I cannot make a bus (based off the DM74LS245 chip). Is there a way to make a tri-state buffer?

EDIT: Note - I don't know much about logic, and it's possible that the thing I want to make isn't a tri-state buffer, but that's what I think it is.

Here are the elements in the app I'm using:

Stuff in the App 1 Stuff in the App 2

Last Thing in the App

  • 2
    \$\begingroup\$ what are the elemental building blocks of Smart Logic Simulator? \$\endgroup\$
    – vicatcu
    Jul 11, 2019 at 2:38
  • \$\begingroup\$ i just added some images with all the components (mind the ad) \$\endgroup\$ Jul 11, 2019 at 12:34
  • \$\begingroup\$ I had built the SN74LS245 in a program called Digital Works and was able to get the desired behavior, but when I tried it in Logism it failed to connect or disconnect and to change direction. You can refer to my question on this subject here: electronics.stackexchange.com/q/450917/215954 \$\endgroup\$ Jul 31, 2019 at 11:03

2 Answers 2


A tristate inverter has truth table:

enable, in, out
0, 0, z
0, 1, z
1, 0, 1
1, 1, 0

You can build such a thing with CMOS transistors. The pull up network has two PMOS in series, and ther pull down network has two NMOS in series. In connects to the lower NMOS and the higher PMOS, and the complement of enable goes to the other two transistors. That looks like this:


simulate this circuit – Schematic created using CircuitLab

You can build other variations on this by introducing inverters in various ways.

  • \$\begingroup\$ i dont think making stuff with cmos, pmos, nmos, etc. is possible with the somewhat limited elements i have. im not even sure if what i asked for is what i need \$\endgroup\$ Jul 11, 2019 at 14:09
  • 2
    \$\begingroup\$ you might be better served asking the developers of the Smart Logic Simulator app directly, e.g. on their Facebook page facebook.com/SmartLogicSimulator \$\endgroup\$
    – vicatcu
    Jul 11, 2019 at 14:36
  • \$\begingroup\$ @vicatcu or indeed by using a better-suited tool for the task at hand \$\endgroup\$ Jul 11, 2019 at 15:08
  • \$\begingroup\$ @Richard the Spacecat what software would you recommend? \$\endgroup\$ Jul 11, 2019 at 15:33
  • \$\begingroup\$ Logisim perhaps? It was made for this kind of thing. It's however PC only afaik, not sure if there's anything decent enough available for mobile. :| \$\endgroup\$ Jul 11, 2019 at 17:26

I decided to just use Logism. It's much more advanced than what I was using before, and itll make things better such as not having to compensate 2 2-input and gates to make a 4-input and gate. Props to Richard the Spacecat!


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.