DISPLY.HLP					Written by Andy Patrick.
						Written 4-Mar-81
						Updated 9-Jun-81

This file, DISPLY.HLP replaces the earlier NEWBRY.HLP.

VT100.OBJ now contains display routines (like NEWBRY.OBJ) to drive the
DIGITAL VT100 VDU in ANSII mode.
NEWBRY.OBJ contains the following procedures designed to drive a NEWBURY VDU.
They were all derived from the original procedures for the MDS screen,
written by Phil Rawlins, and have the same names. See SCREEN.PLM and T21LIB.HLP

BACKSPACE
CLEAR$LINE
CLEAR$REST$OF$SCREEN
CLEAR$SCREEN
CURSOR$ABS
DISPLAY

BACKSPACE   Written by Andy Patrick, 4-Mar-81.
	BACKSPACE: PROCEDURE (NO$OF$CHARS) EXTERNAL;
	DECLARE NO$OF$CHARS BYTE;
	END BACKSPACE;
	Moves the cursor NO$OF$CHARS to the left from its current position.
	The NEWBURY will wrap around if the left margin is reached but in the
	VT100 the cusor will stop at the left margin.

CLEAR$LINE Written 4-Mar-81.
	CLEAR$LINE: PROCEDURE (XPOSN,YPOSN) EXTERNAL;
	DECLARE (XPOSN,YPOSN) BYTE;
	END CLEAR$LINE;
	Positions the cursor at the absolute coordinates XPOSN YPOSN and
	deletes from the cursor to the right hand margin.


CLEAR$REST$OF$SCREEN  Written by Andy Patrick, 4-Mar-81.
	CLEAR$REST$OF$SCREEN: PROCEDURE (XPOSN,YPOSN) EXTERNAL;
	DECLARE (XPOSN,YPOSN) BYTE;
	END CLEAR$REST$OF$SCREEN;
	Clears the screen from the specified position where :
	XPOSN is the number of chars from the lhs of the screen (0 to 79),
	YPOSN is the number of lines down from the top of the screen (0 to 23).
	The cursor is moved to XPOSN,YPOSN.


CLEAR$SCREEN  Written by Andy Patrick, 4-Mar-81.
	CLEAR$SCREEN: PROCEDURE EXTERNAL;
	END CLEAR$SCREEN;
	Clears the whole screen when called. In the NEWBURY  the cursor is
	positioned in the top left hand corner (position 0,0).  In the VT100
	the cursor is not moved.


CURSOR$ABS   Written by Andy Patrick, 4-Mar-81.
	CURSOR$ABS: PROCEDURE (XPOSN,YPOSN) EXTERNAL;
	DECLARE (XPOSN,YPOSN) BYTE;
	END CURSOR$ABS;
	Positions the cursor at the absolute co-ordinate XPOSN,YPOSN.
	Position (0,0) is at the top left hand side of the screen. XPOSN is
	the character position, YPOSN is the line position.
	NEWBURY NOTE:
	      If XPOSN > max then the cursor will appear on the next line down,
	      if YPOSN > max then the top line(s)  will be lost if the NEWBURY
	      is in roll mode. In page mode YPOSN is effectively mod 24.
	VT100 NOTE:
	      If XPOSN > max then the cursor will stop at the right hand margin.
	      If YPOSN > max the cursor will stop at the lower margin.


DISPLAY   Written by Andy Patrick, 4-Mar-81, changed 9-Jun-81.
	DISPLAY: PROCEDURE (XPOSN,YPOSN,TEXT$ADDR) EXTERNAL;
	DECLARE (XPOSN,YPOSN) BYTE, TEXT$ADDR ADDRESS;
	END DISPLAY;
	Moves the cursor to the co-ordinate (XPOSN,YPOSN) on the screen and
	writes the text given by the address TEXT$ADDR. The top left hand
	corner has co-ordinate (0,0). Bottom right hand corner has co-ordinate
	79,23 in the NEWBURY, the VT100 depends on how the various modes are set.
	If the most significant bit of YPOSN is set then it is cleared before
	the cursor is positioned and the rest of the line is deleted.
	If the text string is terminated by a null byte - 00H - then
	<CR,LF> is output after the string. If it is terminated by the value
	80H then no other characters are output (uses ATYPE - see T21LIB.HLP).
	The cursor is left at the end of the string (including the CRLF).

