300(C)

Syntax

300s [ +12 ] [ -n ] [ -dt,l,c ]

Description

The 300 command supports special functions and optimizes the use of the DASI 300 (GSI 300 or DTC 300) terminal; 300s performs the same functions for the DASI 300s (GSI 300s or DTC 300s) terminal. It converts half-line forward, half-line reverse, and full-line reverse motions to the correct vertical motions. In the following discussion of the 300 command, it should be noted that unless your system contains the text processing software, references to certain commands (for example, nroff, neqn, eqn, etc.) will not work. It also attempts to draw Greek letters and other special symbols. It permits convenient use of 12-pitch text. It also reduces printing time by between 5% and 70%. The 300 command can be used to print equations neatly, in the sequence:

neqn file ... | nroff | 300

The behavior of 300 can be modified by the optional flag arguments to handle 12-pitch text, fractional line spacings, messages, and delays.

+12

permits use of 12-pitch, 6 lines/inch text. DASI 300 terminals normally allow only two combinations: 10-pitch, 6 lines/inch, or 12-pitch, 8 lines/inch. To obtain the 12-pitch, 6 lines per inch combination, the user should turn the PITCH switch to 12, and use the +12 option.

-n

controls the size of half-line spacing. A half-line is, by default, equal to 4 vertical plot increments. Because each increment equals 1/48 of an inch, a 10-pitch line-feed requires 8 increments, while a 12-pitch line-feed needs only 6. The first digit of n overrides the default value, thus allowing for individual taste in the appearance of subscripts and superscripts. For example, nroff half-lines could be made to act as quarter-lines by using -2. The user could also obtain appropriate half-lines for 12-pitch, 8 lines/inch mode by using the option -3 alone, having set the PITCH switch to 12-pitch.

-dt,l,c

controls delay factors. The default setting is -d3,90,30. DASI 300 terminals sometimes produce peculiar output when faced with very long lines, too many tab characters, or long strings of blankless, non-identical characters. One null (delay) character is inserted in a line for every set of t tabs, and for every contiguous string of c non-blank, non-tab characters. If a line is longer than l bytes, 1+(total length)/20 nulls are inserted at the end of that line. Items can be omitted from the end of the list, implying use of the default values. Also, a value of zero for t (c) results in two null bytes per tab (character). The former may be needed for C programs, the latter for files like /etc/passwd. Because terminal behavior varies according to the specific characters printed and the load on a system, the user may have to experiment with these values to get correct output. The -d option exists only as a last resort for those few cases that do not otherwise print properly. For example, the file /etc/passwd may be printed using -d3,30,5. The value -d0,1 is a good one to use for C programs that have many levels of indentation.

Note that the delay control interacts heavily with the prevailing carriage return and line-feed delays. The stty(C) modes nl0 cr2 or nl0 cr3 are recommended for most uses.

In many (but not all) cases, the following sequences are equivalent:

nroff -T300 files ... and nroff files ... | 300

nroff -T300-12 files ... and nroff files ... | 300 +12

The use of 300 can thus often be avoided unless special delays or options are required; in a few cases, however, the additional movement optimization of 300 may produce better aligned output.

Warning

Limitations

If your output contains Greek and/or reverse line-feeds, use a friction-feed platen instead of a forms tractor; although good enough for drafts, the latter has a tendency to slip when reversing direction, distorting Greek characters and misaligning the first line of text after one or more reverse line-feeds.

See also