Invisible power pins in CAD
Invisible power pins in CAD
(OP)
Hi guys.
Another tedious CAD question.
A number of packages I've used, Orcad, Cadstar, Vutrax etc. have invisible power pins on stuff like ttl and amplifiers.
The ttl stuff generally has pins defined as Vcc and Gnd.
The analogue stuff has pins defined as Vpos, Vngeg, and Gnd.
4000 series Cmos has pins defined as Vdd and Vss.
To connect the power pins to the gnd and +5V busses, you generally name the buss as "GND" and "VCC" or whatever.
With a mix of devices, such as ttl and 4000 cmos this gets a little difficult.
Both sets of devices run off the +5V buss, but the package won't let you give it two different names.
So how do you get around this?
Up until now, I've used a zero ohm resistor so that one side of the resistor is defined as VCC and the other side is defined as VDD.
How are you supposed to do this?
Coz it looks decidedly unusual on the schematic...
rgds
Zeit.
Another tedious CAD question.
A number of packages I've used, Orcad, Cadstar, Vutrax etc. have invisible power pins on stuff like ttl and amplifiers.
The ttl stuff generally has pins defined as Vcc and Gnd.
The analogue stuff has pins defined as Vpos, Vngeg, and Gnd.
4000 series Cmos has pins defined as Vdd and Vss.
To connect the power pins to the gnd and +5V busses, you generally name the buss as "GND" and "VCC" or whatever.
With a mix of devices, such as ttl and 4000 cmos this gets a little difficult.
Both sets of devices run off the +5V buss, but the package won't let you give it two different names.
So how do you get around this?
Up until now, I've used a zero ohm resistor so that one side of the resistor is defined as VCC and the other side is defined as VDD.
How are you supposed to do this?
Coz it looks decidedly unusual on the schematic...
rgds
Zeit.





RE: Invisible power pins in CAD
You should however always be able to change the names on your parts! Often You could have three or four vcc busses and that you may want some parts on different power nets. This means you MUST be able to specify this. Look at the part definitions as this is where that is done.
RE: Invisible power pins in CAD
Personally, I have found that in the long run, this feature makes circuit troubleshooting more difficult as it isn't obvious from the circuit diagram where the power pins are or what they are connected to. I usually place all of the gates in one symbol package and leave the power pins on the symbol to avoid later confusion.
RE: Invisible power pins in CAD
Dan
Owner
http://www.Hi-TecDesigns.com
RE: Invisible power pins in CAD
RE: Invisible power pins in CAD
Now about that GND symbol...
RE: Invisible power pins in CAD
You can also on a more general level edit the properties of the part itself (double-click the part while in the part editor) and enable the display of the pin names and numbers.
This is all explained in the help menus of OrCAD.
RE: Invisible power pins in CAD
RE: Invisible power pins in CAD
RE: Invisible power pins in CAD
Otherwise can't you just make a schematic connection between Vcc and Vdd, or whatever other node or global?
In any case, you can't escape verifying the netlist before going to the layout package.
RE: Invisible power pins in CAD
Can't join Vcc and Vdd global signals to the same net.
The CadStar schematic capture utility throws a wobbly & gets all upset... thus the 0R resistor.
One of my favourite bugs with Orcad was placing 74 series symbols too close together so that the gnd and vcc invisible pins got connected together.
A little difficult to debug the first time you meet it...
And don't get me started about the time it connected all the signals on a keyboard interface together because one signal on the schematic crossed at just the wrong place. Lots of green wires on that pcb...
RE: Invisible power pins in CAD
Is this an old version of Cadstar?
RE: Invisible power pins in CAD
1998.