Text Mode

UMBC CMSC 211

Text Mode

To display text of 80 x 25 or 2,000 characters takes two bytes per character. Obviously, the one byte is holds the ASCII code. It is followed by an attribute byte. The format for the attribute byte is:

Bl is foreground blink
rgb is the red, green, and blue of the background color
I is intensity
rgb is the red, green, and blue of the foreground color

The colors are coded as:

000	Black (Intense be dark grey)
001	Blue
010	Green
011	Cyan
100	Red
101	Magenta
110	Brown (Intense is yellow)
111	Light Gray (Intense is white)

INT 10h BIOS calls for Text Mode

The most commonly used for our purposes are text mode 3 and graphics mode 12h (VGA 640 x 480 pixels, 16 colors)

Set Video Mode

Input is:
ah = 00h
al = desired video mode

Set Display Page

Input is:
ah = 05h
al = display page number

Get Video Mode and Display Page at once

Input is:
ah = 0Fh

Output is:
al = current video mode
ah = chars per line
bh = display page

Display of Characters

Display Character and Attribute, NO cursor change Input is:
ah = 09h
al = ASCII character
bl = attribute
bh = display page (0 - 3, usually 0) cx = number of copies to display (1, probably)

Display Character using Present Attribute and Advance Cursor

Input is:
ah = 0Eh
al = ASCII character
bh = display page (0 - 3, usually 0)

Get Get Character and attribute at Cursor Position

Input is:
ah = 08h
bh = display page

Output is:
al = ASCII character
ah = attribute

Cursor Manipulations

Set Cursor Position Input is:
ah = 02h
dh = row ( - 24)
dl = column (0 - 79)
bh = display page ( 0 3; 0 probably works)

Get Cursor Position

Input is:
ah = 0eh
bh = display page

Output is:
dh = row
dl = column

Scrolling

Scroll Window Input is:
ah = 06h (scroll up)
or ah = 07h (scroll down)

al = number of lines to scroll (0 to clear window)
ch = row number of upper left-hand corner ( 0 - 24 )
cl = column number of upper-left hand corner ( 0 - 79 )
dh = row number of lower right-hand corner ( 0 - 24 )
dl = column number of lower right-and corner ( 0 - 79 )
bh = attribute for cleared lines

Hardware I/O

Hardware I/O is vry simple. the 80X86 recognizes 2¹⁶ or 65,536 I/O ports. The instructions are:

in	ax or al, port	; Read a word or byte from port
out	port, ax or al	; Write a word or byte to port

NOTE: There is no relationship between ports and interrupt numbers!

A device can use several ports, data ports, status ports, and control ports