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39 lines
3.0 KiB
39 lines
3.0 KiB
Eagle Plugin Implementation Notes. 2017 Russell Oliver
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Below is some notes on the correspondence between Eagle schematics and symbols libraries and the
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KiCad equivalent.
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Eagle libraries are a many to many listing of symbols and footprints connected by a device set and
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device definitions. They are embedded in the schematic and board files if there are used, and
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therefore the schematic symbols and footprints can be recovered from either file.
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An Eagle device set definition is the information needed to represent a physical part at the
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schematic level including the functional gates of the device. Each gate is lists the symbol to be
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displayed for that gate. This is equivalent to a KiCad symbol unit. Since the symbol is defined
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outside of the device set, multiple devices sets in the library can use the same symbol for a gate.
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Lower to a device set, is the device definition. This establishes the link between the schematic
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symbols and a physical part through the 'connect' elements. These map the symbol pins for each gate
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to the physical pins provided by the package (footprint) definition. An Eagle Symbol outlines the
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layout of graphical of items including pins. Pins for multi gate symbols are generally labelled
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per their function, i.e. input / output. An Eagle symbol pin is not numbered but merely labelled. A
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connect element gives the pad number for each pin found in that gate. Therefore the equivalent
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KiCad pin number is read from the connect element pad number. Since an Eagle gate is equivalent to
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a KiCad symbol unit, the graphical items for that unit will be copied from the Eagle symbol for
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that gate and will be unique for that unit. This will yield duplication of the graphical elements
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if the same symbol is used for multiple gates but the conversion will be complete.
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An Eagle sheet contains a list of instances, which are equivalent to KiCad schematic component
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entries. An instance describes the part, the gate used and its location on the sheet. This is
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translated into the equivalent KiCad symbol with the given unit number.
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Eagle 'plain' items describe graphical items with no electrical connection, such as note text,
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lines etc. Of importance is the use of wire elements to describe both electrical connections and
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graphical items. A wire element will act as an electrical connection when defined within a net and
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segment. Anywhere else it is a graphical line. The layer for the wire element will change the
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displayed colour for the wire. Connections between regular wires and busses occur when a wire ends
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on a bus segment. When translated to KiCad a bus connection symbol is created. Within an Eagle
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schematic there can be multiple sheets in a flat hierarchy. For each sheet, there is a list of
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electrically connected nets. Each net is broken up into graphically connected segments, defined by
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a list of wires and labels. Labels remain associate with wires of that net segment, even if they
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are not located on a wire element. This necessitates the movement of such a label to the nearest
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wire segment within KiCad.
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