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13.5 Modification by Patching
Modification by patching is used in installing Word Processing for printers
that require special control strings or modifications to one of Word
Processing printers drivers, and for achieving refinements in installation,
such as supporting special features of specific non-daisy printers.
Since basic installation is achieved with the INSTALL program as described
previously, most users should not need to patch.
"Patching" means modifying Xerox Word Processing by changing the
contents of bytes in XWS.COM. Patching is accomplished with INSTALL's
patcher. The rest of this section is written primarily for the reader who
already understands patching, usually an assembly language programmer.
Listings in Appendix:
Appendix B of this manual contains an absolute
assembly listing of the user-patchable portions of Xerox Word Processing
containing all printer-related patch items for non-daisy printers, plus many
used f or both daisy and non-daisy printers.
The listing is commented heavily; read it for a detailed description of each
item. The following paragraphs
give
a general description of the module,
and hit a few high points of the details, but do not attempt to duplicate the
detailed information contained in the program comments.
The module whose listing is supplied was combined with the rest of the
program with a linking loader after assembly; it contains external
references whose values are not shown in the listing. Generally, these are in
locations there will be no need to change.
Modifications in the printer patch area are used to support optional printer
features, to install unusual printers which are similar to, but not exactly,
"Teletype-like", and do not support ETX/ ACK
type communications
protocols or has no protocols. Modifications in the printer patch area are
also used to handle unusual installation requirements with regard to the
transmission of characters from (as required by communications protocol
Section 13.2.2) and to the printer.
This manual does not cover patching to support the features of daisy-wheel
printers. The INSTALL program performs complete installation to support
all available features of the common daisy wheel and similar printers.
Patching for such printers is extremely complex due to the interaction of
many features and the requirements of bidirectional printing, variable
character width, and variable line height.
However, all aspects of transmission of characters to and from serial daisy
wheel and similar printers are accessible and documented in this section.
REFERENCE
13-20
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