## Using the Keyboard and Video Display

OS-9 has many features to expand the capability of the computer keyboard and video display. The video display has screen pause, upper/lower case, and graphics functions. The keyboard can generate all ASCII characters and has a type-ahead feature that permits you to enter data before requested by a program (except if the disk is running because interrupts are temporarily disabled). Appendix B, VDG Display System Functions of this manual is a list of the characters and codes that can be generated from the keyboard. The keyboard/video display can be used as a file known by the name “/TERM”.

### Video Display Functions

The computer uses reverse video (green letters in a black box) to represent lower-case letters. Normally they are not used, so you have to turn them on if you want to use them with the command:

    tmode -upc

The screen pause feature stops programs after 16 lines have been displayed. Output will continue if you hit any key. Normally this feature is on. It can be turned on or off with the tmode command as follows:

    tmode -pause              turns pause mode off
    tmode pause               turns pause mode on

The display system also has a complete set of commands to emulate commercial data terminals, plus a complete set of graphics commands. These are described in detail in Appendix C, Key Definitions With Hexadecimal Values.

### Keyboard Shift and Control Functions

Two keys are used in combination with other keys to change their meaning. The SHIFT key selects between upper case and lower case letters or punctuation, and the CTRL[3] key can be used to generate “control characters”.

The keyboard has a shift lock function similar to a typewriter's, which is normally “locked”. The keyboard's shift lock may be reversed by depressing the control key and 0 keys simultaneously. The shift lock only affects the letter (A-Z) keys. When the keyboard is locked, these keys generate upper case letters, and lower case only if the SHIFT key is depressed. When the keyboard is unlocked, the reverse is true, e.g., lower case letters are generated unless the SHIFT key is depressed at the same time as a letter key.

### Control Key Functions

There are a number of useful control functions that can be generated from the keyboard. Many of these functions use “control keys” which are generated by simultaneously depressing the CTRL key plus some other key. For example, to generate the character for CONTROL+D press the CTRL and D keys at the same time.

CONTROL+A

  Repeat previous input line. The last line entered will be redisplayed but not processed, with the cursor positioned at the end of the line. You may hit return to enter the line, or edit the line by backspacing, typing over characters to correct them, and entering control A again to redisplay the edited line.

CONTROL+D

  Redisplay present input on next line.

CONTROL+W

  Display Wait - This will temporarily halt output to the display so the screen can be read before the data scrolls off. Output is resumed when any other key is hit.

CONTROL+0

  Shift lock. Reverses present shift lock state.

BREAK (or CONTROL+E)

  Program abort - Stops the current running program

SHIFT+BREAK (or CONTROL+C)

  Interrupt - Reactivates Shell while keeping program running as background task.

CONTROL+BREAK (ESCAPE)

  End-of-File - This key is used to send an end-of-file to programs that read input from the terminal in place of a disk or tape file. It must be the first character on the line in order for it to be recognized.

← (or CONTROL+H)

  Backspace - erase previous character

SHIFT+← (or CONTROL+X)

  Line Delete - erases the entire current line.

[3] The Color Computer models 1 & 2, and the Dragon 64 computers use the CLEAR key as there is no CTRL key.