The CP-6 system has an extensive set of commands which enable the terminal user to edit terminal input, control terminal output, and control the course of program execution. The most widely used features are summarized below.
Typeahead
CP-6 terminal I :0 routines allow terminal users to type input during the time computation is taking place or output is being typed at the terminal. Such input is not echoed to the terminal immediately. Instead. the data is stored until the proper time for its utilization; that is, the time following programmatic requests for input. Thus, in the script typed at the terminal, input appears following the query asking for it even if the input was typed sometime previously.
Terminal Profiles
CP-6 terminal profiles identify terminal types. Profiles contain a detailed description of terminal characteristics, such as character code set, timing information, a list of the terminal's features, and how to perform cursor positioning. Profiles may be defined by the installation, using SUPER. Definition files for most terminals normally used with CP-6 are included in the installation materials provided by Bull. A listing of profile names is included in Appendix F.
The user may specify the name of the profile during or after logging on, or may have a specific profile invoked automatically during log-on.
The CP-6 system provides character code conversion for the ASCII character set, some variations of ASCII, and bit-paired and typewriter-paired ASCII APL. The system can automatically adjust to the ASCII or ASCII APL character sets during the connection process.
The character set may also be changed during the session via the ESC $ escape sequence, a PRO FI L E command or programmatically.
12-2 Terminal Profiles CE26-02_DRAFT
CP-6 Time-Sharing
. --.- _. -.--- - ---" - ---.-----_ ..
_--Output Efficiency
Positioning functions directed to the terminals are optimized. The effects of space, backspace, horizontal tab, carriage return, and line feed characters (and combinations of these characters) are analyzed before sending positioning information to the terminal. Then the optimal combination of the carriage return, line feed, space, backspace. direct cursor position, absolute tab, cursor forward, cursor back, cursor up, and cursor down functions is sent to the terminal.
This optimization process can result in greatly increased terminal throughput. This technique also allows any program to take advantage of advanced device features without knowing what device is being used, thereby providing a high degree of device independence.
Several timing algorithms are supplied to determine when timing fill characters are sent to the terminal. These characters provide delay for positioning of the carriage before and/or after positioning functions (e.g., carriage return, line feed, absolute tab), and after erase and control functions. The algorithms are further tailored to the device by way of timing parameters specified in the profile, yielding optimal output efficiency.
The CP-6 system supports flow control for buffered devices using the DCI/DC3
(XON /XOFF). ETX/ ACK, and CTS (Clear To Send) disciplines. This support means data can be sent to the device at the maximum rate the device can accept data.
Transparent Mode
A program may request that no translation or other processing be performed by CP-6 terminal I/O. In this case, characters are moved between program and terminal without change in the bit structure. This mode is useful for connecting to special equipment, tape cassettes, plotters, paper tape, or other computers.
Pagination and Formatting
The CP-6 system offers two types of pagination: logical and device.
Logical pagination is similar to line printer pagination. System service calls, I B EX commands, or a line printer compatible forms description enable the user to establish page parameters, including page width and length, top and bottom margins, and the channel number to line number correspondence for skip to channel operations. When the end of the logical page is reached, a page break is performed, and a heading is issued. Headings generated include user specified text and reflect any user-supplied indentation, page numbering, and space-after parameter values. Input and output lines are folded to fit within the page width. All VFC (Vertical Format Control) codes legal for a line printer are also handled for terminals. Typing ESC L causes a page break. Typing ESC - signifies the terminal is positioned at the perforation.
Simulated perforations may be printed on non-perforated paper to ease fanfolding or cutting at page boundaries.
CE26-02_DRAFT Pagination and Formatting 12-3
CP-6 Time-Sharing
Device pagination allows the operator of a screen terminal to view output before it is scrolled off or over-written. Output is halted after each screenful of data. The operator then types a carriage return to continue. The relative pagination mode computes the page position relative to the last read, eliminating page halts when the user is interactive and not generating full pages of contiguous output. Device pagination may be turned on or off at any time by typing ESC A .
Terminal Input Functions
The CP-6 system supports a number of terminal input functions that allow the user great flexibility in preparing terminal input. Terminal input functions define special characters and escape sequences that allow the user to edit terminal input, control input conversion, control tab simulation and perform miscellaneous functions. Table 12-1 lists the CP-6 terminal input functions.
Editing Terminal Input
Visual fidelity is maintained on most screen terminals. When character insertion, replacement, and deletion is performed, the image on the screen is constantly updated to the current contents of the input record. As this update is performed in place, a minimum of space is consumed on the screen, thereby minimizing the scrolling off of important information. Since characters cannot be erased on hardcopy terminals, editing causes characters to be printed that note the updates to the record. However, all editing functions work on both screen and hardcopy terminals.
Terminal editing may also be used on program-supplied data. The user program may pass a record to the CP-6 system, allow the operator to edit the data, and send it back to the user program. The CP-6 EDIT and APL processors use this feature to provide terminal editing for data in their files.
Controls Over Input Conversion
Character conversions are generally done automatically by the CP-6 system in the proper way for each terminal type. However, the input conversion functions allow the user to control upper and lower case conversions.
Tab Simulation
The tab simulation functions control the effect of simulated tab stops on the terminal and on the program.
The user may also establish the setting of the simulated tab stops using either programmatic or execution control commands.
12-4 Tab Simulation CE26-02_DRAFT
CP-6 Time-Sharing User Input Functions
Users may define their own input functions by using 1M P. Input functions define special characters and escape sequences that the CP-6 system is to interpret. The interpretation yields character strings to be processed as input text and / or system special characters and escape sequences, or as output text. For example, the following 1M P command defines an input function that generates a tab setting command when a