Several important memory unit addresses

1. system clock address

0000: 046ch --	4 bytes	The clock Counter automatically adds 1 to every time the clock is interrupted. When the system starts, the value is the number of clock interruptions from midnight to the present. When the Count reaches 24 hours, it is set to 0 and the byte of 0000: 0470h is set to 1.
0000: 0470 h --	1 byte	This byte is set to 1 at midnight.

See Int 8 h (clock interruption)

2. display the feature data address

0000: 0449 h --	1 byte	Current Display Mode
0000: 044ah --	1 word	Number of characters per line (number of columns)
0000: 044ch --	1 word	Display the number of buffer bytes
0000: 044eh --	1 word	The amount of moving the current display page in the display buffer
0000: 0450 h --	8 words	The position of the cursor in the display page. The high byte is the row, and the low byte is the column.
0000: 0460 h --	1 word	The shape of the current cursor. The high byte indicates the cursor goes online, and the low byte indicates the cursor goes offline.
0000: 0462 h --	1 byte	Current display page
0000: 0463 h --	1 word	Port address of the CRT control index register
0000: 0465 h --	1 byte	Current Value of the mode register in the CRT controller
0000: 0466 h --	1 byte	Current Value of the color register in the CRT controller

See Int 10 h (display service interruption)

3. display the buffer address

A000: 0000 -- display content in the content Graphic Display Mode

Table 1 Definition of Display Properties for a monochrome display

Background attributes

Foreground attributes

7	6	5	4	3	2	1	0
Blink				Bright

B000: 0000 --	H characters	Displays text information on the black-and-white display. The low byte in each word is the ASCII code of the character, and the high byte is its attribute.
B800: 0000 --	H	The display buffer of the Color Monitor. Its character display content is the same as that of the former

Table 2 display Attribute Table for black and white displays

Background attributes			Foreground attributes
7 6 5 4	Attribute		3 2 1 0	Attribute

0 0 0 0 Black 0 1 1 1 Reverse 1 0 0 0 Blink 1 1 1 1 Reverse blink

0 0 0 0 Black 0 0 0 1 Underlined 0 1 1 1 Normal 1 0 0 1 Bright underlined 1 1 1 1 Bright

Table 3 Definition of display attributes of a Color Monitor

Background attributes

Foreground attributes

7	6	5	4	3	2	1	0
Blink	Red	Green	Blue	Bright	Red	Green	Blue

Table 4 display attributes of a color display

Background attributes			Foreground attributes
7 6 5 4	Attribute		3 2 1 0	Attribute

0 0 0 0 Black 0 0 0 1 Blue 0 0 1 0 Green 0 0 1 1 Cyan 0 1 0 0 Red 0 1 0 1 Magenta 0 1 1 0 Brown 0 1 1 1 White 1 0 0 0 Black blink 1 0 0 1 Blue blink 1 0 1 0 Green blink 1 0 1 1 Cyan blink 1 1 0 0 Red blink 1 1 0 1 Magenta blink 1 1 1 0 Brown blink 1 1 1 1 White blink

0 0 0 0 Black 0 0 0 1 Blue 0 0 1 0 Green 0 0 1 1 Cyan 0 1 0 0 Red 0 1 0 1 Magenta 0 1 1 0 Brown 0 1 1 1 White 1 0 0 0 Dark gray 1 0 0 1 Light blue 1 0 1 0 Light Green 1 0 1 1 Light cyan 1 1 0 0 Light red 1 1 0 1 Light magenta 1 1 1 0 Yellow 1 1 1 1 Bright White

4. keyboard address

0000: 0417 h --	1 word	Current keyboard status table (see figureA6.1)
0000: 041ah --	1 word	The header pointing to the keyboard buffer.
0000: 041ch --	1 word	Pointing to the end of the Keyboard Buffer
0000: 041eh --	16 words	Default Keyboard Buffer Byte Count
0000: 0471 h --	1 byte	The value is set to 80 h. When int 9 h finds that the key combination is pressed ^ break
0000: 0480 h --	1 word	Queue header of the Keyboard Buffer
0000: 0482 h --	1 word	End of the Keyboard Buffer Queue
0000: 0496 h --	1 word	If it is 4 = 1, the extended keyboard is installed.

Figure A6.1 keyboard status table

See Int 09 h, int 16 h, and INT 1bh (^ break)

5. interrupted vector table

0000: 0000 h --

1024 bytes

For more information, see the functions of int 21 h: 25 h (set the interrupt number entry address) and 35 h (read the interrupt number entry address)

6. System Configuration

0000: 0400 h --	4 words	Serial Port (COM1 ~ Com4) base address
0000: 0408 h --	4 words	Printer Port (LPT1 ~ Lpt4) base address
0000: 0410 h --	1 word	System Device table (see figureA6.2)
0000: 0413 h --	1 word	General memory bytes (in K)

Figure A6.2 system device table

See Int 11 h (Read Device Configuration) and INT 12 h (read General memory size)

7. Hard drive

0000: 043eh --	1 byte	Drive flag, its position 0 ~ 3 corresponds to drive a, drive B, drive C, and drive d respectively. You can use int 11 h to know the number of disk drives in the system.
0000: 043fh --	1 byte	Drive Motor sign, its position 0 ~ 3 corresponds to drive a, drive B, drive C, and drive d respectively. If one is 1, the drive corresponding to it is rotating.
0000: 0440 h --	1 byte	The start time of the drive motor. The default value is about 2 seconds. You can set this value through INT 13 H.
0000: 0441 h --	1 byte	Latest disk operation status 00 h-no error 01 H-invalid command 02 h-address mark not found 03 h-disk write protection (floppy disk) 04 H-fan location discovery 08h-dma overrun (floppy disk) 09h-dma goes beyond 64 K 10 h-Incorrect CRC data 20 h-controller failure 40 h-search failed 80 h-disk timeout

See Int 08 h (clock interruption), INT 13 H (Disk Service Interruption), and INT 1eh (Disk parameter table ).

8. Rom data

F000: e000h --	Changed	BIOS version description
F000: fffeh --	1 byte	System mode code
F000: ffffh --	1 byte	System Sub-mode code (meaning of the Code in the mode and sub-mode are omitted)

9. Address of other content

0000: 0478 h --	4 bytes	LPT1 and lpt2 cycle counters. It affects the printer's timeout judgment.
0000: 047ch --	4 bytes	COM1 ~ Com4. It determines the number of times the modem or online Status Register is read.
0000: 0500 h --	1 byte	Indicates the status of the screen printing operation: 0 -- Successful 1 -- Printing 0ffh -- Failed
0000: 0504 h --	1 byte	Drive symbols for a single disk system: 0-a and 1-B

See Int 05 h (screen printing), int 14 h (interrupted serial communication service), and INT 17 h (printer service)