Xerox 701P21091 manual Tape codes, Packed data formats, Record formats

Specifying input parameters

Tape codes

Tape codes that are recognized by the DP EPS 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.

The “Offline specifications” appendix 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.

Using LCDS Print Description Language 2-9