In order to make our schematics useful to end users, it's important to assign useful names to your pins.
Gnd pins should be assigned the name 'Gnd' (or sometimes VSS, depending on the naming conventions you want to use), and SPI pins should be assigned useful names like MISO, MOSI, SCK, and CS, etc.
Most of the time, the datasheet will contain a schematic symbol we can copy, though, including pin names. The GA1A1S202WP datasheet doesn't contain one, but there are only four pins so it's easy to figure out a basic layout and pin names.
Renaming pins in the symbol editor is the same as renaming pads in the package editor ... you simply select the 'Name' tool from the toolbar (highlighted in yellow below) ...
... then click on your pin, and assign a unique name to it via the popup dialogue box:
In this case, our device as the following four pins:
- Pin 1 = GND
- Pin 2 = GND
- Pin 3 = IO (Analog Output)
- Pin 4 = VCC (the power supply for this device)
Lets start with VCC, renaming P$1 to 'VCC', which should give you the following results:
... and after clicking 'OK' ...
Now do the same for P$2, renaming it to 'IO', which will result in the following:
Shared Pin Names
This leaves us with the last two pins, both of which are 'Gnd', but it also introduces a problem.
Like pads on your package, pins must all have unique names
When you have several pins with the same name and functionality (which is often the case with 'Gnd', 'VCC, 'VDD', etc.), we can assign the common name followed by the '@' symbol, and a unique number.
When Eagle renders our symbol on the schematic the @1, @2, etc., part of the name will be hidden, and only the common name preceding the @ will be shown.
Try it out by assign the following names to the last two pins in our symbol:
which should give you something similar to the image below:
That's it! You have the absolute minimum requirement for your symbol, and we can move on to the final step in the part design process, the 'Device' ... but as with the package, it's worth spending a few more minutes and do things properly in our new symbol.