Data Sheet

Schematic Capture

This presents us with the Make Device dialogue form, where we can customize the part. All

fields throughout this wizard have context sensitive help associated with them, accessed by

clicking on the question at the top right and then on the field in question. However, the only

items we need to deal with here are the Device Name and the Reference Prefix. The device

name should be MCP23008 and the reference prefix should be ‘U’.

The reference prefix serves to categorize parts for Bill of Materials Output and is

also used in annotation. These are fairly standard across the industry with ‘R’

denoting resistors, ‘C’ for capacitors, ‘U’ for IC’s and so on.

Use the Next button at the bottom of the dialogue to move onto the next screen.

Adding Footprints

In a previous section of the documentation we saw how to quickly add a footprint to a schematic

part. This is useful for small passives and simple parts but, when we are creating a device we

need to follow a more complete procedure. This ensures not only that we have a correct

mapping between the pins on the component and the pads on the footprint but also allows us to

better handle power pins.

From the screen on the Make Device dialogue form click on the Add/Edit button to launch the

Visual Packaging Tool. The first thing we need to do is to find the footprint we want to use so

click on the Add button at the top of the dialogue form.

The 'Add' button in the Packaging Tool

This brings up the package browser dialogue which we covered earlier in the documentation.

Assuming that we want the surface mount package, type SOP18 in the Keywords field and then

double click on the part in the results list to select it.

Selecting the SO18W from the package library

The Visual Packaging Tool will now look something like the following screenshot.