Format of ASCUR parameter block:
Offset	Size	Description	)
 00h	WORD	0003h (length of following data)
 02h	BYTE	cursor start line (00h = top of cell, FFh = keep current shape)
 03h	BYTE	cursor stop line
 04h	BYTE	cursor attribute
		00h normal
		01h hidden
		02h left-arrow (requires start = 2 and stop = bottom of cell)
		03h right-arrow (requires start = 2 and stop = bottom of cell)
Notes:	no cursor is shown if the start line is greater than the stop line
	the alphanumeric cursor is hidden after each mode change
SeeAlso: #03882,INT 10/AH=01h