next up previous contents index
Next: Computer Graphics Exchange (CGX) Up: Symbol File Formats Previous: CIF Format Extensions   Contents   Index


Native Symbol File Format

Native symbols use an extension to the CIF format, with one symbol per file. Each file can contain two cell definitions: one for physical geometry, and the second for electrical (schematic) data. The physical information is found first. If there is no electrical information, the electrical cell definition is not written. The parser will also recognize schematic files from the Jspice3 program, which have a similar format, but no physical cell definition. Xic will write an empty physical cell definition if there is no physical information (electrical only).

The basic file layout is shown below.

(Symbol symbol_name);
(RCS_ID);
(program_version date);
(PHYSICAL);
(RESOLUTION 1000);
9 symbol_name;
DS 0 1 1;
physical data ...
DF;
E
(ELECTRICAL);
(RESOLUTION 1000);
9 symbol_name;
DS 0 1 1;
electrical data ...
DF;
E
SPICE listing

The first line is a CIF comment giving the symbol name. The second line is a comment providing an ID field to be used with the RCS code control program. The RCS program is used to manage large projects with multiple designers. An optional comment line containing the creating program version and creation date follows. The next line is a CIF comment containing the word ``PHYSICAL''. This indicates that the following cell definition contains physical data. If this line is not found, some time consuming tests are performed to figure out what exactly is in the file.

An optional ``(RESOLUTION 1000);'' comment line follows. This indicates that coordinates in the physical part of the file use 1000 units per micron. If the line is not present, 100 units per micron is assumed. This was the default for early versions of Xic, and follows from the implicit CIF assumption. The use of resolutions other than 100 represents an extension of the CIF syntax.

The electrical part of the cell is optional, and starts with a CIF comment containing the word ``ELECTRICAL'', followed by the resolution comment and the electrical cell description. Either cell description can be empty, i.e., a DS 0 1 1; line followed by DF; and E. Finally, if the cell was written in schematic mode and is a top-level cell (containing no terminal nodes) a SPICE listing of the circuit is added to the bottom of the cell file. Such files can be read directly into the WRspice program for simulation. The SPICE listing has no relevance to Xic.

The format of the Physical cell data adheres to the extended CIF described in the preceding sections. Electrical cell descriptions use the same extensions, however the array extension never appears, as arrays are not available in electrical mode. The major difference in the files is the large number of properties assigned in electrical mode.


next up previous contents index
Next: Computer Graphics Exchange (CGX) Up: Symbol File Formats Previous: CIF Format Extensions   Contents   Index
Stephen R. Whiteley 2006-10-23