No power Nets from hidden power Pins on 74LS04 devices

Using KiCAD 5.1.4-1 release build on Windows 10. Placed Schematic 74LS04 using 74xx symbols library. Run Annotate and got Reference U6A. Then Assigned footprint and built netlist and then run PcbNew and loaded Netlist. Part appears no problem but no connections to power pins 7 and 14.
My Schematic has a GND symbol connected to a Power Flag both selected from “power” symbol standard list. (Simulary for VCC).
I have tried everything including selecting or not selecting the “do not show hidden pins” on the left hand side menu and in deperation placing an additional part using the same same U6 reference but the “G” unit outline selected. (the latter gives an error message as there are duplicate parts with the same reference).
The only way I have got it to work is to make a new part with visible power pins but this will be a lot of work as there are many different logic ICs used.
Any help very much appreciated!

Sorry, bad reading :slight_smile:

Placing the power unit is the correct approach. Sounds like your reference is wrong. Not sure why you refer to hidden pins, this symbol does not use them.

Are you still using V4 libraries, V5.1.x uses a 7 unit symbol. The G unit is the power component and its pins are visible

Ok if I understand you correctly in addition to placing the A logic unit of the chip I should also place the G power unit using the same reference address? Is this correct?

1 Like

Yes, that’s right…

1 Like

many thanks problem solved

There are some misleading V4 tutorials on the Internet that explain the old and now fortunately dropped, hidden power pins way

As @bobc confirmed, yes you need both units.

Additionally, it is best practice to include all units by putting the unused units in the corner (or separate page) of your schematic labeled “Unused Gates”, “Unused Units”, or something similar. Most discrete logic ICs suggest in the datasheet to tie the inputs to unused gates to either VCC or GND to avoid floating inputs to cause switching noise at random times within the IC. Some datasheets specify either VCC or GND, others suggest either is OK. Having the unused gates allow you to terminate the inputs, and if you decide you need to use another gate you have on the schematic which gates are available without adding components to your design.


This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.