Using Electric 9-8: Pad Frame Generation

Chapter IX: TOOLS

| ## 8: Pad Frame Generation |

The Pad Frame generator reads a disk file and places a ring of pads around your chip. The pads are contained in a separate library, and are copied into the current library to construct the pad frame.

The format of the pad frame disk file is as follows:

`celllibrary LIBRARYFILE` | ; Identifies the file with the pads
`facet PADFRAMEFACET` | ; Creates a facet to hold the pad frame
`core COREFACET` | ; Places your circuit in the center of the pad frame
`align PADFACET INPUTPORT OUTPUTPORT` | ; Defines input and output ports on pads
`place PADFACET [GAP] [PORTASSOCIATION]` | ; Places a pad into the pad frame
`rotate DIRECTION` | ; Turns the corner in pad placement

The file must have exactly one `celllibrary` and `facet` statement, as they identify the pad library and the pad frame facet. The file may have only one `core` statement to place your top-level circuit inside of the pad frame. If there is no `core` statement, then pads are placed without any circuit in the middle.

The `align` statement is used to identify connection points on the pads that will be used for placement. Each pad should have an input and an output port that define the edges of the pad. These ports are typically the on the power or ground rails that run through the pad. When placing pads, the output port of one pad is aligned with the input port of the next pad.

Each pad that is placed with a `place` statement is aligned with the previous pad according to the alignment factor. A gap can be given in the placement that spreads the two pads by the specified distance. For example, the statement:

`place padIn gap=100`
requests that the "padIn" pad be placed so that its input port is 100 lambda units away from the previous pad's output port.

If a core facet has been given, you can also indicate wiring between the pads and the core ports. This is done by having one or more port associations in the `place` statements. The format of a port association is simply `PADPORT = COREPORT`. For example, the statement:

`place padOut tap=y`
indicates that the "tap" port on the placed pad will connect to the "y" port on the core facet.

The `rotate` statement rotates subsequent pads by the specified amount. The statement has only two forms: `rotate c` to rotate clockwise, and `rotate cc` to rotate counterclockwise.

Here is an example of a pad frame disk file, with the finished layout:

| `; specify the cell library with the pads celllibrary pads.elib ; create a facet called "padframe" facet padframe ; place this facet as the "core" core mychip ; set the alignment of the pads ; (specifying input and output port names) align padCorner vdd-in vdd-out align padPower vdd-in vdd-out align padGround vdd-in vdd-out align padIn vdd-in vdd-out align padOut vdd-in vdd-out ; place the top edge of pads, ; starting with upper-left place padCorner place padPower tap=vdd place padOut tap=out4 ; place the right edge of pads rotate c place padCorner place padOut tap=out3 place padOut tap=out2 ; place the bottom edge of pads rotate c place padCorner place padOut tap=out1 place padGround tap=gnd ; place the left edge of pads rotate c place padCorner place padIn tap=a2 place padIn tap=a1`

This file places 8 pads in a ring (2 on each side) and also places corner "pads" for making bends. The input pads connect to the 2 input ports "a1" and "a2". The output pads connect to the 4 output ports "out1", "out2", "out3", and "out4" The power and ground pads connect to the "vdd" and "gnd" ports.

Connections between pads and ports of the core facet use Unrouted arcs (from the Generic technology, see Section 7-9). These arcs can be converted to real geometry with the river router. To do this, you must select arcs on one side of the pad frame and use the River-Route subcommand of the Routing command of the Tools menu (see Section 9-5 for more on routing). Since the river router always pushes geometry to the left and bottom, this will work for the left and bottom sides only. To route the top and right sides, you must rotate the entire circuit (select everything and rotate 180 degrees). After routing the top and right (now left and bottom) you can rotate the circuit back to its original position. The finished layout is shown here, fully instantiated. |

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