SECTION 14
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 ULTRA 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 ULTRA 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
•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.
