Xerox ALLY PLUSTM 6287 - Manual (Page 113)

SCS DATA STREAMS
General Information
SNA character string (SCS) controls are EBCDIC codes embedded by the
host system in a document and used for formatting the data sent to devices
such as printers and CRT displays. The AGILE 6287 ALLY PLUS achieves
its emulation of IBM printers by translating the SCS codes into PFSs
(programmable function strings) that the printer can use to format data.
To use SCS controls, the ALLY PLUS must be defined to the host
computer as an SNA Type 1 logical unit. Type 1 logical units use SCS
codes to control data formatting.
Presentation Surface:
SNA Character String Definitions
Devices that use SCS data formatting can be represented logically by a two-
dimensional area called the presentation surface. The SCS control codes
direct the formatting of data on a presentation surface.
The presentation surface can be viewed as a two-dimensional matrix of
character positions. Each character position is referenced by line and
column coordinates. The presentation surface represents a single page of
printed output.
 Presentation Surface Width and Depth determine the maximum
physical dimensions of the page (maximum number of characters per
line, maximum number of lines per page).
 Margins are the logical boundaries within which data will actually
be printed. If the data sent by the control unit exceeds these margins,
the data may not be printed.
 Maximum Presentation Line is the number of the last physical line
on the page.
 Maximum Presentation Position is the number of the rightmost
character position on the physical page.
 Presentation Position is the line and column number of the current
position on the page. The presentation position indicates where the
next character will be printed on the page.
SECTION 7