I'm working with a schematic in Eagle and I use IC's with different types of power pins. I connect VDD to VCC to +5V and I connect GND to VSS to zero volts.
When I look at the ERC, I receive warnings as follows:
WARNING: Sheet 1/1: POWER Pin IC1 VCC connected to VDD
WARNING: Sheet 1/1: POWER Pin IC1 GND connected to VSS
WARNING: Sheet 1/1: POWER Pin IC5 V+ connected to VDD
WARNING: Sheet 1/1: POWER Pin IC5 GND connected to VSS
When I switch over to PCB manufacturing mode, it seems that not all the pins are connected.
My schematic has a microcontroller, CMOS IC's and a 555 timer.
Do I need to add resistors between each of the different power supply designations? I'm trying to be legal so that no electrical software complains.
Best Answer
In schematic editors, a 'net', that is a set of nodes connected together, has a name, and is identified by that name. Therefore the 'VCC' and 'VDD' nets are distinct. If a wire is used to connect them, this will cause a logical problem for the editor. Different editors have different behaviour in these circumstances. Some will automatically rename one net, some will leave the nets unconnected.
There are several solutions
a) Connect them by a component, such as a 0-ohm resistor. This is wasteful if the only reason is to get round net naming issues, though the odd 0-ohm link in power supplies can be handy for debugging, allowing various bits of the circuit to be isolated
b) Choose a unified net name as one of the comments suggests. Rename everything to 'VCC' or the like. I don't like this as labels like 'VCC' and 'VDD' already have semantic meaning, and can cause confusion with the data sheet, at least, they confuse me.
c) Name the nets on the board for what they are. I tend to filter supplies, so end up with nets called '+5v_in', '+4.8v_fil', '+4.5v_fil2' etc, so I know where I am.