lt spice digital logic gates

Thread Starter

denison

Joined Oct 13, 2018
137
I found the A and B inputs for the xor gate in lt spice. The output always shows 1v or 0v regardless of the voltage applied at the inputs.
There are other terminals on this gate which ltspice does not explain there purpose.
Does anybody know what these other terminals are for and how to use them? I suspect they may somehow give the user the option to select other voltages for the logic levels.
 

eetech00

Joined Jun 8, 2013
2,058
I found the A and B inputs for the xor gate in lt spice. The output always shows 1v or 0v regardless of the voltage applied at the inputs.
There are other terminals on this gate which ltspice does not explain there purpose.
Does anybody know what these other terminals are for and how to use them? I suspect they may somehow give the user the option to select other voltages for the logic levels.
Hi

Read the LTspice Help for "A devices". LTspice Help explains the optional parameters.

This is an Idealized behavioral gate and is intended to be wrapped by other circuit components to create a complete functional gate. You can set the logic levels with the Vhigh and Vlow parameters.

eT
 

Alec_t

Joined Sep 17, 2013
11,755
.... and to set those optional parameters, right-click on the gate symbol and enter appropriate text in the Value field.
 

Thread Starter

denison

Joined Oct 13, 2018
137
Hi

Read the LTspice Help for "A devices". LTspice Help explains the optional parameters.

This is an Idealized behavioral gate and is intended to be wrapped by other circuit components to create a complete functional gate. You can set the logic levels with the Vhigh and Vlow parameters.

eT
cannot find anything in help for A devices. There is info under special functions which gives terminal 8 as the device common. There are 8 terminals on all the logic gates according to this info. The gates are not numbered on the schematic but it still shows 8 terminals.
Can anyone on this forum please send me back a schematic of the xor gate with the 8 terminals numbered? Also then the description of each numbered terminal and I should be able then to work out for myself how to use this gate in a simulation. I suspect then that the vhigh and vlow parameters will then be 2 of the terminals that I am not using. Common will be another terminal I am not using leaving only 1 other unexplained terminal.
 

eetech00

Joined Jun 8, 2013
2,058
HI

Yes..they are "special function" devices or "A" devices in LTspice speak :D

None of these devices have "numbers". They are all primitive elements to be used in creating your own logic devices.
You can use them as is but you'll have to customize their operating parameters. The help file has a table listing the settable attributes.
To set a attribute, place the symbol on the schematic, rht-clk on the symbol to open the symbol's attribute page.
Dbl-clk in the "Value2" field and then type Vhigh=5 Vlow=0 to set the device for 5v logic. Do the same for any other attributes you want to set.

If you want to number pins, you'll have to create your own custom symbol to use with the A device.

Or, instead, you can do it this easier way...

You can just use an existing device library, like a CD4000 library, where all that work has already been done.
You can get the library from the LTspice Yahoo Group or maybe from someone on this forum who has a copy.

eT
 

Thread Starter

denison

Joined Oct 13, 2018
137
HI

Yes..they are "special function" devices or "A" devices in LTspice speak :D

None of these devices have "numbers". They are all primitive elements to be used in creating your own logic devices.
You can use them as is but you'll have to customize their operating parameters. The help file has a table listing the settable attributes.
To set a attribute, place the symbol on the schematic, rht-clk on the symbol to open the symbol's attribute page.
Dbl-clk in the "Value2" field and then type Vhigh=5 Vlow=0 to set the device for 5v logic. Do the same for any other attributes you want to set.

If you want to number pins, you'll have to create your own custom symbol to use with the A device.

Or, instead, you can do it this easier way...

You can just use an existing device library, like a CD4000 library, where all that work has already been done.
You can get the library from the LTspice Yahoo Group or maybe from someone on this forum who has a copy.

eT
I also use tina-ti which is texas instruments simulation program and have found the logic gates I am looking for there. These are much easier to use with numbered terminals etc and because TI make a lot of logic gates you can get the simulation that will match exactly the actual product.
I don't think linear technology(analog devices) make any logic gates.
Thanks for the input anyway. Ltspice is easier to use than tina-ti.
 

eetech00

Joined Jun 8, 2013
2,058
I also use tina-ti which is texas instruments simulation program and have found the logic gates I am looking for there. These are much easier to use with numbered terminals etc and because TI make a lot of logic gates you can get the simulation that will match exactly the actual product.
I don't think linear technology(analog devices) make any logic gates.
Thanks for the input anyway. Ltspice is easier to use than tina-ti.
Hi

Ok...whatever works best for you.

I have Tina also but the original version from DesignSoft.

eT
 
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