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SPECIFYING INPUT PARAMETERS
4-66 XEROX DOCUPRINT 180 LPS PDL REFERENCE
Packed data formats
Six-bit characters may be written onto a 9-track tape in a 4-by-3
packed (or compressed) format. That is, four 6-bit data bytes are
compressed into three 8-bit data bytes. Two methods of packing
these bits together exist. One method is used by Honeywell 6000
users (T4X3), while Honeywell 2000 users employ a slightly different
method of packing (T4X3H2).
Whenever an unpacking method is included in the JDL, the system
unpacks the characters before data processing. Each 6-bit character
is extracted, and two high-order zeros are appended. Normally, after
data is unpacked, it must be translated. The character code set is
defined in the CODE parameter of the VOLUME command. For a 4-
by-3 unpacking method, the data is generally encoded in BCD, and
one of the three standard BCD CODE parameters (H2BCD, H6BCD,
and IBMBCD) can be used.
The “Offline specifications” appendix shows an example of how 6-bit
characters packed in the T4X3 method (also T4X3H2) are unpacked
and then translated to ASCII by the system.
Record formats
All tape records input to the printing system are either blocked or
unblocked with a fixed length, a variable length, or an undefined
format. The PDL commands BLOCK and RECORD define the format
of the input data. Tape label contents may also describe blocking and
record structure and in some cases override BLOCK and RECORD
commands specified in the JDL source file. These labels are
described in this chapter and in the Xerox LPS Tape Formats
Manual.
Record structure
A record is arbitrarily divided into two portions: operating system and
user. The operating system portion of the record contains information
supplied by the host operating or spooling system. The user's portion
of the record contains information provided by the application or
user's program running on the host system. The boundary between
the two portions of the record is traditionally between the record
length and printer carriage control (PCC) field. If there is no record
length field, there is no operating system portion of the record. The
PDL commands that define the components of a record are
described in the “Input record characteristics—RECORD command”
section of this chapter.