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Using Tristate Buffer 74LS126


I tried to use the tristate buffer IC 74LS126 in the schematic which is having 3 pins in the symbol as input, control and output and I have given proper signals at these pins, but after giving ERC it showed 2 errors as power supply terminals unconnected, even though there are no power supply terminlas (Vcc and GND) in the symbol.

Please guide me how I can make this IC work accurately in the schematic.

Thanks in advance
<span style="background-color: rgb(250, 250, 250); line-height: 1.428571429;">Harish Bhat N.
</span><span style="background-color: rgb(250, 250, 250); line-height: 1.428571429;">MITE Moodabidire</span>

Oscad Schematic-Creation-and-Simulation 00-01 min None sec 18-04-14, 2:12 p.m. harishvb81


Hi, You need to click on the button "show hidden pins" on the schematic editor. If I remember correctly, this button is available on the toolbar on the left. (second last button)
18-04-14, 2:24 p.m. rakhiwarriar


I have connected Vcc and Gnd using show hidden pin option and then connected, but after simulation there is a fatal error in ngspice and the error is 74ls126.sub no such file or directory include statement failed.

<span style="line-height: 1.428571429;">

<span style="line-height: 1.428571429;">Harish Bhat</span>

18-04-14, 5:09 p.m. harishvb81

Hi, from which library did you take this component? I mean did you take it from digital or digitalXspice?
19-04-14, 10:41 a.m. rakhiwarriar

Please note the following:
(1) The reason for the error is that you would have enabled the option "Prefix IC and U with X" option while creating netlist. You should not do that. Disable that option and create the netlist.
(2) If the component you are using is not taken from the libraries digitalSpice or digitalXspice or linearSpice (or any library ending with Spice), then it does not have support for simulation.
(3) <span style="line-height: 1.428571429;">Please take D_TRISTATE component from digitalXspice and use it as the tristate buffer in your circuit. It has the same functionality as 74LS126.</span>
19-04-14, 10:52 a.m. rakhiwarriar

Let me know if Ngspice gives an error/warning - can't find init file.
19-04-14, 10:53 a.m. rakhiwarriar

Yes madam ngspice is showing can't find init file error

Very sorry for the delay in response

24-04-14, 9:26 p.m. harishvb81

Dear Harish,

There was problem with digital simulation in Oscad windows installer which has been sorted out and it will soon be uploaded to website. I will share with you file

For time being you can follow the below steps.
0.Take backup of old spice folder under C:\OSCAD
1. Unzip the new file.
2. Copy extracted spice folder into C:\
3.Change the system path variable for spice from C:\OSCAD\spice to C:\spice

Please let us know if you face any error after doing above steps.

25-04-14, 6:19 p.m. fahim

Sir after installing new spice folder as per the procedure told by you, once again there is a simulation error in ngspice

which states, unable to find definition of model 0 74ls126 and two vplot I have used in the schematic are showing error as no such vector v(5) and no such vector v(4).

Please guide me and thanks a lot for all your support till now

Harish Bhat

25-04-14, 8:44 p.m. harishvb81
As I suggested earlier, please use D_TRISTATE <span style="background-color: rgb(250, 250, 250);">component from digitalXspice and use it as the tristate buffer in your circuit. It has the same functionality as 74LS126. If you use the component 74LS126, it won't work.</span>
25-04-14, 10:39 p.m. rakhiwarriar

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Here is link to new folder
25-04-14, 6:23 p.m. fahim

Thank You all,  I am able to use simple NMOS for the same functionality I was not giving reference starting with letter M I was giving it as default Q

Thanks a lot

Harish Bhat

29-04-14, 8:15 p.m. harishvb81

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