Note that to use this program you must have at least one of the (optional) RAM cartridges for the DeskJet or DeskJet PLUS printer. Without this option the DeskJet printer cannot accept soft fonts and you have to use the lcat (1) program (supplied in this distribution) that is slower but works with the base configuration of the DeskJet family.
The program is designed to be used as a filter, but under MSDOS this cannot be done (pipes are considered text streams and there is no way to suppress output processing; so tabs are converted to spaces etc.). For this reason the -O flag is provided to specify an output file.
If you use the default fonts (times) be sure to supply troff with the correct font width tables (see vwidth(1)).
The MSDOS version of Vcat keeps (in a primitive sort of way) information about the fonts that have been sent to the printer in a file (font.tbl) in the font directory. Thus if you call vcat twice with the same input the second file will be printed much faster as it will not have to download any fonts to the printer.
If you switch the printer off you'll have to remove that file, a utility (fcache.bat) may be used to flush the cache. If the cache file is missing vcat will complain but will work anyway assuming that the cache is clear (at the end of the run vcat will recreate the cache file, so its ok to remove the cache file if you are not sure about its contents).
The UNIX version keeps only a per job record.
Under UNIX vcat creates the soft fonts from the vfonts on the fly so you don't need to keep two versions of the same files (no, you can't erase the vfonts once you've created the DeskJet soft fonts, vcat needs both!). The UNIX version keeps the font file in the vfont directory. Under MSDOS (due to memory and processor speed limitations) its not feasable to perform the conversion on the fly, we thus have to generate the DeskJet soft fonts in advance and store them in a directory (called djfonts) under the vfont directory. In this case the font.tbl is kept in the djfonts directory.
troff -t -man /usr/man/man1/ls.1v | vcat > /dev/lp
The program assumes that the printer can hold up to 16 fonts. This is arbitrary (but experience with a DeskJet PLUS with one 256K byte cartridge, shows that this is a good guess). If you have a different configuration you will have to use a different number and recompile. Ideally vcat should use the font size information in the header and determine how much memory is available on the printer.
Unfortunately vcat does not support ligature expansion (ligatures are single letters that represent letter combination like fi, ffi fl etc.). If your font doesn't have ligatures and you want to use vcat, then be sure to tell troff not to use ligatures (specify the command .lg 0 in the beginning of your troff file). Note that by default troff assumes that you do want ligatures generated.