QANDA

QANDA is a PDP-12 subroutine designed for interactive textual communication using the VR12 display. Written in LINC mode, it enables users to display text, pose questions to the viewer, facilitate editing of input, and capture responses.

The subroutine requires a PDP-12 computer equipped with a VC12 LINCscope control, a VR12 CRT display, and a Teletype. It is invoked via a JMP QAINIT instruction, which initializes an answer buffer and takes pointers to both the text string to be displayed and the answer buffer. The text string can incorporate special characters to control display formatting, such as line breaks (RETURN), defining question field lengths (<), and selecting full-size (F) or half-size (H) character formats.

User input is received from the Teletype keyboard, converted to 6-bit code, and displayed on the scope, replacing underline characters in the answer fields. Special input characters provide editing and navigation capabilities; for instance, RUBOUT deletes the preceding character, RETURN moves to the next question field (or the first if at the last), < moves the cursor left, and > moves it right.

QANDA offers an entry point, QARFSH, to refresh the display without re-initializing the answer buffer, allowing calling programs to perform periodic checks or display messages. The subroutine returns to a specific address once the typist has completed their input (signaled by LINE FEED or RETURN without question fields).

Regarding system usage, QANDA resides in the same LINC lower memory segment as the calling sequence and utilizes index registers 1-6, which must be managed by the calling program if used between display refreshes. It has display limitations, supporting a maximum of 44 half-size or 22 full-size characters horizontally and 13 lines vertically. QANDA also calls the GETKBD LINC Teletype input subroutine.