Xerox 4112-4127 Enterprise Printing System-192 - Manual (Page 117)

Specifying input parameters
Using LCDS Print Description Language 2-9
Tape codes
Tape codes that are recognized by the FreeFlow Print Server
LCDS systems are EBCDIC, ASCII, and several versions of
BCD. If these codes are not sufficient for a particular tape, you
may create a new code translation table or modify (customize)
an existing code translation table. Tables that show the
correspondence between standard recording codes and printed
characters are in Appendix C, “Character code assignment
tables,” in this manual. Within a JDL, tape codes are selected by
the CODE parameter of the VOLUME command.
Packed data formats
Six bit characters may be written onto a 9 track or 36-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.
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.
Appendix D, “Offline specifications,” shows an example of how 6
bit characters that are packed in the T4X3 or T4X3H2 method
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 BLOCK and RECORD commands define the format
of the input data. Tape label contents may also describe blocking
and record structure, and in some cases they override BLOCK
and RECORD commands that are specified in the JDL source
file. These labels are described in this chapter and in the Xerox
LPS Tape Formats Manual.