memory.lst

A Programmer s Reference to BIOS, DOS, and Third-Party Calls

--------B-M00400013--------------------------
MEM 0040h:0013h - BASE MEMORY SIZE IN KBYTES
Size:	WORD
SeeAlso: INT 12
--------b-M00400015--------------------------
MEM 0040h:0015h - PC, XT - ADAPTER MEMORY SIZE IN KBYTES
Size:	WORD
--------b-M00400015--------------------------
MEM 0040h:0015h U - AT - MANUFACTURING TEST SCRATCH PAD
Size:	BYTE
--------K-M00400015--------------------------
MEM 0040h:0015h - Compaq Deskpro 386 - PREVIOUS SCAN CODE
Size:	BYTE
--------b-M00400016--------------------------
MEM 0040h:0016h U - AT - MANUFACTURING TEST SCRATCH PAD
Size:	BYTE
--------b-M00400016--------------------------
MEM 0040h:0016h U - PS/2 Model 30 - BIOS CONTROL FLAGS
Size:	BYTE
--------K-M00400016--------------------------
MEM 0040h:0016h - Compaq Deskpro 386 - KEYCLICK VOLUME
Size:	BYTE
Range:	00h-7Fh
--------K-M00400017--------------------------
MEM 0040h:0017h - KEYBOARD - STATUS FLAGS 1
Size:	BYTE
SeeAlso: MEM 0040h:0018h,INT 16/AH=02h,MEM 0040h:0096h

Bitfields for keyboard status flags 1:
Bit(s)	Description	(Table M0010)
 7	INSert active
 6	Caps Lock active
 5	Num Lock active
 4	Scroll Lock active
 3	either Alt pressed
 2	either Ctrl pressed
 1	Left Shift pressed
 0	Right Shift pressed
SeeAlso: #M0011,#00587
--------K-M00400018--------------------------
MEM 0040h:0018h - KEYBOARD - STATUS FLAGS 2
Size:	BYTE
SeeAlso: MEM 0040h:0017h,INT 16/AH=12h

Bitfields for keyboard status flags 2 :
Bit(s)	Description	(Table M0011)
 7	INSert pressed
 6	Caps Lock pressed
 5	Num Lock pressed
 4	Scroll Lock pressed
 3	Pause state active
 2	Sys Req pressed
 1	Left Alt pressed
 0	Left Ctrl pressed
SeeAlso: #M0010,#00588
--------K-M00400019--------------------------
MEM 0040h:0019h - KEYBOARD - ALT-nnn KEYPAD WORKSPACE
Size:	BYTE
Desc:	holds the current value of an Alt-NNN keypad sequence; when Alt is
	  released and this byte is non-zero, the appropriate character is
	  placed in the keyboard buffer
SeeAlso: INT 16/AH=00h,MEM 0040h:001Ah
--------K-M0040001A--------------------------
MEM 0040h:001Ah - KEYBOARD - POINTER TO NEXT CHARACTER IN KEYBOARD BUFFER
Size:	WORD
SeeAlso: MEM 0040h:001Ch,MEM 0040h:0080h,MEM 0040h:0082h,INT 16/AH=00h
--------K-M0040001C--------------------------
MEM 0040h:001Ch - KEYBOARD - POINTER TO FIRST FREE SLOT IN KEYBOARD BUFFER
Size:	WORD
SeeAlso: MEM 0040h:001Ah,MEM 0040h:001Eh,MEM 0040h:0080h,MEM 0040h:0082h
SeeAlso: INT 16/AH=00h
--------K-M0040001E--------------------------
MEM 0040h:001Eh - KEYBOARD - DEFAULT KEYBOARD CIRCULAR BUFFER
Size:	16 WORDs
SeeAlso: MEM 0040h:001Ah,MEM 0040h:001Ch,MEM 0040h:0080h,MEM 0040h:0082h
SeeAlso: INT 16/AH=00h,INT 16/AH=05h
--------B-M0040003E--------------------------
MEM 0040h:003Eh - DISKETTE - RECALIBRATE STATUS
Size:	BYTE
SeeAlso: MEM 0040h:003Fh,MEM 0040h:0040h,INT 13/AH=00h,INT 13/AH=11h

Bitfields for diskette recalibrate status:
Bit(s)	Description	(Table M0012)
 7	diskette hardware interrupt occurred
 6-4	reserved
 3	recalibrate diskette 3 (PC,XT only)
 2	recalibrate diskette 2 (PC,XT only)
 1	recalibrate diskette 1
 0	recalibrate diskette 0
--------B-M0040003F--------------------------
MEM 0040h:003Fh - DISKETTE - MOTOR STATUS
Size:	BYTE
SeeAlso: MEM 0040h:003Eh,MEM 0040h:0040h

Bitfields for diskette motor status:
Bit(s)	Description	(Table M0013)
 7	current operation is write or format, rather than read or verify
 6	reserved (DMA enabled on 82077)
 5-4	diskette drive number selected (0-3)
 3	diskette 3 motor on (PC,XT only)
 2	diskette 2 motor on (PC,XT only)
 1	diskette 1 motor on
 0	diskette 0 motor on
--------B-M00400040--------------------------
MEM 0040h:0040h - DISKETTE - MOTOR TURN-OFF TIMEOUT COUNT
Size:	BYTE
Desc:	number of clock ticks until diskette motor is turned off
Note:	the typical implementation of the timeout is to have the INT 08 
	  handler decrement this byte on every clock tick, and force the
	  diskette motor off if the result is equal to zero
SeeAlso: MEM 0040h:003Eh,MEM 0040h:003Fh,MEM 0040h:0041h,INT 08"IRQ0"
--------B-M00400041--------------------------
MEM 0040h:0041h - DISKETTE - LAST OPERATION STATUS
Size:	BYTE
SeeAlso: MEM 0040h:003Eh,MEM 0040h:0042h,INT 13/AH=01h

Bitfields for diskette last operation status:
Bit(s)	Description	(Table M0014)
 7	drive not ready
 6	seek error
 5	general controller failure
 4-0	error reason
	00h no error
	01h invalid request/parameter
	02h address mark not found
	03h write-protect error
	04h sector not found
	06h diskette change line active
	08h DMA overrun
	09h DMA across 64k boundary
	0Ch media type unknown
	10h CRC error on read
Note:	the following values for this byte differ somewhat from the
	  bitfield definition above:
	    30h drive does not support media sense
	    31h no media in drive
	    32h drive does not support media type
	    AAh diskette drive not ready
--------B-M00400042--------------------------
MEM 0040h:0042h - DISK - FLOPPY/HARD DRIVE STATUS/COMMAND BYTES
Size:	7 BYTEs
SeeAlso: MEM 0040h:0041h

    42h BYTE	XT: command byte to hard disk controller
		AT: write precompensation cylinder number / 4
    43h	BYTE	XT: bit 5 = drive number, bits 3-0=head number
		AT: sector count
    44h BYTE	XT: bits 6,7 = high bits of track, bits 5-0 = start sector-1
		AT: starting sector
    45h BYTE	low byte of track number
    46h BYTE	XT: sector count
		AT: high bits of track number
    47h BYTE	XT: controlbyte from HD parameters (step rate,...)
		AT: 101DHHHH, D=drive number, HHHH=head number
		    bit 7 = ECC mode (1)
		    bit 6 = unknown (0)
		    bit 5 = 512 byte sectors (1)
		    bit 4 = drive number
		    bit 3-0 head number
    48h BYTE	XT: INT 13h subfunction number
		AT: command byte to hard disk controller
SeeAlso: CALL F000h:211Eh
--------B-M00400042--------------------------
MEM 0040h:0042h - DISK CONTROLLER STATUS REGISTER 0
Size:	BYTE
SeeAlso: MEM 0040h:0043h

Bitfields for diskette controller status register 0:
Bit(s)	Description	(Table M0015)
 7-6	interrupt code
	00 normal completion
	01 abnormal termination during execution
	10 invalid command
	11 abnormal termination: ready line on/diskette change
 5	requested seek complete
 4	drive fault
 3	drive not ready
 2	head state at time of interrupt
 1-0	selected drive (drives 2&3 on PC,XT only)
SeeAlso: #M0016
--------B-M00400043--------------------------
MEM 0040h:0043h - DISK CONTROLLER STATUS REGISTER 1
Size:	BYTE
SeeAlso: MEM 0040h:0042h,MEM 0040h:0044h

Bitfields for diskette controller status register 0:
Bit(s)	Description	(Table M0016)
 7	attempted access beyon last cylinder
 6	unused
 5	CRC error on read
 4	DMA overrun
 3	unused
 2	data error
 1	disk write protected
 0	missing address mark
SeeAlso: #M0015,#M0017
--------B-M00400044--------------------------
MEM 0040h:0044h - DISK CONTROLLER STATUS REGISTER 2
Size:	BYTE
SeeAlso: MEM 0040h:0043h

Bitfields for diskette controller status register 0:
Bit(s)	Description	(Table M0017)
 7	unused
 6	found deleted data address mark
 5	CRC error in data field
 4	wrong cylinder number read
 3	verify equal
 2	can't find sector matching verify condition
 1	bad cylinder
 0	unable to find address mark
SeeAlso: #M0016
--------V-M00400049--------------------------
MEM 0040h:0049h - VIDEO - CURRENT VIDEO MODE
Size:	BYTE
SeeAlso: MEM 0040h:004Ah,INT 10/AH=00h
--------V-M0040004A--------------------------
MEM 0040h:004Ah - VIDEO - COLUMNS ON SCREEN
Size:	WORD
SeeAlso: MEM 0040h:0049h,MEM 0040h:004Ch,MEM 0040h:004Eh,INT 10/AH=0Fh
--------V-M0040004C--------------------------
MEM 0040h:004Ch - VIDEO - PAGE (REGEN BUFFER) SIZE IN BYTES
Size:	WORD
SeeAlso: MEM 0040h:004Ah,MEM 0040h:004Eh,MEM 0040h:0050h
--------V-M0040004E--------------------------
MEM 0040h:004Eh - VIDEO - CURRENT PAGE START ADDRESS IN REGEN BUFFER
Size:	WORD
SeeAlso: MEM 0040h:004Ch,MEM 0040h:0050h,MEM 0040h:0062h,INT 10/AH=05h
--------V-M00400050--------------------------
MEM 0040h:0050h - VIDEO - CURSOR POSITIONS
Size:	8 WORDs
Desc:	contains row and column position for the cursors on each of eight
	  video pages
SeeAlso: MEM 0040h:004Eh,MEM 0040h:0060h,INT 10/AH=02h
--------V-M00400060--------------------------
MEM 0040h:0060h - VIDEO - CURSOR TYPE
Size:	WORD	(big-endian)
Desc:	contains cursor start scan line and cursor end scan line
SeeAlso: MEM 0040h:0050h,MEM 0040h:0062h,INT 10/AH=03h
--------V-M00400062--------------------------
MEM 0040h:0062h - VIDEO - CURRENT PAGE NUMBER
Size:	BYTE
SeeAlso: MEM 0040h:004Eh,MEM 0040h:0063h,INT 10/AH=05h
--------V-M00400063--------------------------
MEM 0040h:0063h - VIDEO - CRT CONTROLLER BASE I/O PORT ADDRESS
Size:	WORD
Note:	normally 03B4h for mono and 03D4h for color video boards
SeeAlso: MEM 0040h:0065h,MEM 0040h:0066h
--------V-M00400065--------------------------
MEM 0040h:0065h - VIDEO - CURRENT MODE SELECT REGISTER
Size:	BYTE
Desc:	contains last value written to I/O port 03B8h / 03D8h
SeeAlso: MEM 0040h:0063h,MEM 0040h:0066h

Bitfields for current video mode select register:
Bit(s)	Description	(Table M0018)
 7-6	unused
 5	attribute bit 7 controls blinking instead of background
 4	mode 6 graphics in monochrome
 3	video signal enabled
 2	monochrome
 1	graphics
 0	80x25 text
--------V-M00400066--------------------------
MEM 0040h:0066h - VIDEO - CURRENT SETTING OF CGA PALETTE REGISTER
Size:	BYTE
Desc:	contains the last value written to I/O port 03D9h
SeeAlso: MEM 0040h:0063h,MEM 0040h:0065h,INT 10h/AH=0Bh/BH=01h

Bitfields for CGA palette register:
Bit(s)	Description	(Table M0019)
 7-6	unused
 5	palette (0/1)
 4	intense background colors in text mode
 3	intense border color (40x25) / background color (mode 5)
 2	red
 1	green
 0	blue
----------M00400067--------------------------
MEM 0040h:0067h - PC only - CASSETTE TIME COUNT
Size:	WORD
SeeAlso: INT 15/AH=00h
----------M00400067--------------------------
MEM 0040h:0067h - RESET RESTART ADDRESS
Size:	DWORD
Desc:	this address stores the address at which to resume execution after a
	  CPU reset (or jump to F000h:FFF0h) when certain magic values are
	  stored at 0040h:0072h or in CMOS RAM location 0Fh
SeeAlso: MEM 0040h:0072h,MEM F000h:FFF0h,CMOS 0Fh,INT 19
----------M00400069--------------------------
MEM 0040h:0069h	- CASSETTE (PC only) - CASSETTE CRC REGISTER
Size:	WORD
SeeAlso: MEM 0040h:006Bh"CASSETTE",INT 15/AH=02h
----------M00400069--------------------------
MEM 0040h:0069h - V20-XT-BIOS - KEY REPEAT
Size:	BYTE

Bitfields for V20-XT-BIOS key repeat flags:
Bit(s)	Description	(Table M0020)
 7	key repeat disabled
 6	Ctrl-Alt pressed instead of just Alt
----------M0040006B--------------------------
MEM 0040h:006Bh - CASSETTE (PC only) - LAST VALUE READ FROM CASSETTE
Size:	BYTE
SeeAlso: MEM 0040h:0069h"CASSETTE",INT 15/AH=02h
----------M0040006B--------------------------
MEM 0040h:006Bh - POST LAST UNEXPECTED INTERRUPT (XT and later)
Size:	BYTE
Desc:	this is a bitmask of IRQs which have occurred while the corresponding
	  interrupt vector points at the default system BIOS handler
	  (bit 0 = IRQ0 to bit 7 = IRQ7; bit 2 = IRQ8-15 on AT and later)
SeeAlso: INT 0F"IRQ7",INT 70"IRQ8",INT 77"IRQ15"
----------M0040006C--------------------------
MEM 0040h:006Ch - TIMER TICKS SINCE MIDNIGHT
Size:	DWORD
Desc:	updated approximately every 55 milliseconds by the BIOS INT 08 handler
SeeAlso: MEM 0040h:0070h,INT 08"IRQ0",INT 1A/AH=00h
----------M00400070--------------------------
MEM 0040h:0070h - TIMER OVERFLOW
Size:	BYTE
Desc:	non-zero if timer has counted past midnight since last call to
	  INT 1A/AH=00h
Note:	the original IBM BIOS, and thus most other BIOSes, sets this byte to
	  01h at midnight; a few (such as the Eagle PC-2) increment it each
	  time midnight is passed.  The former behavior results in lost days
	  if multiple midnights pass between "get-time" calls while the machine