This section describes the extensions to the CIF and GDSII formats used by Xic. The CGX file format, designed to be a more efficient replacement for GDSII and released into the public domain by Whiteley Research Inc., is described below as well. The extensions to CIF and GDSII are designed to accommodate the electrical information and certain properties. When strict conformance to the standard format is required, such as when exporting physical layouts to a mask vendor, the Strip For Export button in the Export Control panel should be used to strip out all extensions, leaving only the physical layout.
The GDSII (Stream) format is owned by Cadence, Inc., and is described in documentation available from Cadence (specifically the ``Design Data Translators Reference,'' which is updated periodically), which may be available on the internet.
In Xic, cell names are not limited in length. The cell names can contain any characters valid in a file name with the exception of the semicolon (`;'), which is reserved in the CIF-like syntax used for native cell files. For portability, it is recommended that cell names use only the GDSII allowed characters, which are the alpha-numerics plus `_', `$', and `?'. In older GDSII specifications (release 3), cell names were limited to 32 characters, so it may be wise to observe this limit in Xic.
Archive files created by Xic generally consist of two records, the first containing the physical information, and the second containing electrical information. If there is no electrical information, the second block is not written. Each block is an individual representation of the archive file type, i.e., they each parse as a complete ``file''. GDSII files written in this manner are generally portable to other CAD systems (format extensions appear in the electrical block only), as reading will terminate at the end of the physical block, and the following electrical block will be ignored. However, in specific instances where this proves not to be true, the Strip For Export button, which eliminates the electrical block, should be used.
The same comments apply to OASIS and CGX formats, however CGX is not known to be supported by other CAD vendors at this time.
CIF files use extensions unique to Xic, so will likely not be portable to other CAD systems unless Strip For Export is used. These extensions are described below.