The Unsorted BBS Collection

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Text File | 1993-04-27 | 81KB | 1,686 lines

=========================================== SOURCER REMARKS FILE - BIOS REMARKS =========================================== :::::::::::::::::::::::::::::::: DATA REMARKS :::::::::::::::::::::::::::::::: --------- Data Remarks ----------- -------- comments ignored here -------- 001 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ PRIMARY BIOS DATA AREA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ RS-232 port addresses rs232_1 002 Printer port addresses prn_1 003 Equipment installed info bits equip_install 15 14 13 12 11 10 9 8 \ / game \ / # of print port # of RS-232 ports 0-3 used ports 0-4 7 6 5 4 3 2 1 0 \ / \ / \ / Math | # of video mode RAM uP no disk- at boot up 00=16K dsk ettes 00=EGA/VGA 01=32K driv 1-4 01=CGA-40 10=48K if 0 if bit 10=CGA-80 11=64K 0 = 1 11=MDA-80 (old PCs) Note: bit 13=modem on PC lap-tops bit 2=mouse on MCA & others 004 Manufacturing Test Byte manufactr_test bit 0 = 1 while in test mode MCA systems use other bits during POST operations 005 Base memory size 0-1Meg, 1K steps main_ram_size 006 Manufacturing test error codes error_codes 007 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ KEYBOARD DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Keyboard flag bits keybd_flags_1 7 6 5 4 3 2 1 0 ins- cap num scrl alt ctl lef rig sert --toggles--- --shifts down-- 008 Keyboard flag bits keybd_flags_2 7 6 5 4 insert caps num scroll ------now depressed------ 3 2 1 0 pause sys left right lock request -alt-down- 009 Alt & digit pad number buffr area keybd_alt_num 00A Head ptr of circular key queue keybd_q_head empty if head ptr = tail ptr 00B Tail ptr of circular key queue keybd_q_tail empty if head ptr = tail ptr 00C 15 key queue for keyboard keybd_queue 00D unused 00E █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ DISK DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Recalibrate floppy drive bits dsk_seek_stat 3 2 1 0 drive-3 drive-2 drive-1 drive-0 bit 7 = interrupt flag 00F Motor running status & disk write dsk_motor_stat bit 7=1 disk write in progress bits 6&5 = drive selected 0 to 3 3 2 1 0 drive-3 drive-2 drive-1 drive-0 --------- 1=motor on----------- 010 Motor timer, at 0, turn off motor dsk_motor_tmr 011 Controller return code dsk_ret_code 00h = ok 01h = bad command or parameter 02h = can't find address mark 03h = can't write, protected dsk 04h = sector not found 08h = DMA overrun 09h = DMA attempt over 64K bound 10h = bad CRC on disk read 20h = controller failure 40h = seek failure 80h = timeout, no response 012 Status bytes-disk controller chip dsk_ctrl_stat Note: 7 info bytes returned from controller are saved here. Refer to the NEC uPD 765 chip manual for the specific info, depending on the previous command issued. 013 unused 014 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ VIDEO DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Present display mode(see int 10h) video_mode 015 Number of columns video_columns 016 Video buffer size in bytes video_buf_size Note: size may be rounded up to the nearest 2K boundary. For example, 80x25 mode=4000 bytes, but value may be 4096. 017 Video page offset of the active video_pag_off page, from start of current video segment. 018 Cursor position page 0 video_cur_pos0 bits 15-8=row, bits 7-0=column 019 Cursor position page 1 video_cur_pos1 bits 15-8=row, bits 7-0=column 01A Cursor position page 2 video_cur_pos2 bits 15-8=row, bits 7-0=column 01B Cursor position page 3 video_cur_pos3 bits 15-8=row, bits 7-0=column 01C Cursor position page 4 video_cur_pos4 bits 15-8=row, bits 7-0=column 01D Cursor position page 5 video_cur_pos5 bits 15-8=row, bits 7-0=column 01E Cursor position page 6 video_cur_pos6 bits 15-8=row, bits 7-0=column 01F Cursor position page 7 video_cur_pos7 bits 15-8=row, bits 7-0=column 020 Active cursor, start & end lines video_cur_mode bits 12 to 8 for starting line bits 4 to 0 for ending line 021 Present page video_page 022 Video controller base I/O address video_port 023 Hardware mode register bits video_mode_reg 024 Color set in CGA modes video_color 025 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ GENERAL DATA █ █ Note: next 5 bytes also used █ █ for cassette interface in █ █ the original PC. █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ General use offset pointer @gen_use_ptr 026 General use segment gen_use_seg 027 Unused interrupt occurred gen_int_occurd value holds the IRQ bit 7-0 of the interrupt that occurred 028 Timer, low word, cnts every 55 ms timer_low 029 Timer, high word timer_hi 02A Timer overflowed, set to 1 when timer_rolled more than 24 hours have elapsed 02B Bit 7 set if break key depressed keybd_break 02C Boot (reset) type gen_warm_boot 1234h=warm boot, no memory test 4321h=boot & save memory (PS/2 with MCA only) 02D █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ HARD DISK DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Hard disk status hdsk_status_1 00h = ok 01h = bad command or parameter 02h = can't find address mark 03h = can't write, protected dsk 04h = sector not found 05h = reset failure 07h = activity failure 08h = DMA overrun 09h = DMA attempt over 64K bound 0Ah = bad sector flag 0Bh = removed bad track 0Dh = wrong # of sectors, format 0Eh = removed control data addr mark 0Fh = out of limit DMA arbitration level 10h = bad CRC or ECC, disk read 11h = bad ECC corrected data 20h = controller failure 40h = seek failure 80h = timeout, no response AAh = not ready BBh = error occurred, undefined CCh = write error, selected dsk E0h = error register = 0 FFh = disk sense failure 02E Number of hard disk drives hdsk_count 02F Head control (XT only) hdsk_head_ctrl 030 Hard disk control port (XT only) hdsk_ctrl_port 031 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ I/O PORT TIMER, KEYBOARD DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Countdown timer waits for printer prn_timeout_1 to respond (printer 1) 032 Countdown timer waits for printer prn_timeout_2 to respond 033 Countdown timer waits for RS-232 rs232_timout_1 port to respond (port 1) 034 Countdown timer waits for RS-232 rs232_timout_2 port to respond 035 Ptr to beginning of keybd queue @keybd_begin 036 Ptr to end of keyboard queue @keybd_end 037 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ ADVANCED VIDEO DATA, EGA/VGA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Rows of characters on display - 1 video_rows 038 Number of pixels per charactr * 8 video_pixels 039 Display adapter options video_options bit 7 = clear RAM bits 6,5 = memory on adapter 00 - 64K 01 - 128K 10 - 192K 11 - 256K bit 4 = unused bit 3 = 0 if EGA/VGA active bit 2 = wait for display enable bit 1 = 1 - mono monitor = 0 - color monitor bit 0 = 0 - handle cursor, CGA 03A Switch setting bits from adapter video_switches bits 7-4 = feature connector bits 3-0 = option switches 03B Video save area 1-EGA/VGA control video_1_save bit 7 = 200 line mode bits 6,5 = unused bit 4 = 400 line mode bit 3 = no palette load bit 2 = mono monitor bit 1 = gray scale bit 0 = unused 03C Video save area 2 video_2_save 03D █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ OTHER FLOPPY & HARD DISK DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Last data rate for diskette dsk_data_rate bits 7 & 6 = 00 for 500K bit/sec = 01 for 300K bit/sec = 10 for 250K bit/sec = 11 for 1M bit/sec bits 5 & 4 = step rate Rate at start of operation bits 3 & 2 = 00 for 500K bit/sec = 01 for 300K bit/sec = 10 for 250K bit/sec = 11 for 1M bit/sec 03E Hard disk status hdsk_status_2 03F Hard disk error hdsk_error 040 When the hard disk controller's hdsk_complete task is complete, this byte is set to FFh (from interrupt 76h) 041 Diskette controller information dsk_options bit 6 = 1 Drv 1 type determined 5 = 1 Drv 1 is multi-rate 4 = 1 Drv 1 change detect 2 = 1 Drv 0 type determined 1 = 1 Drv 0 is multi-rate 0 = 1 Drv 0 change detect 042 Media state for diskette drive 0 dsk_media_st0 7 6 5 4 data xfer rate two media 00=500K bit/s step known 01=300K bit/s 10=250K bit/s 11=1M bit/sec 3 2 1 0 unused -----state of drive----- bits floppy drive state 000= 360K in 360K, ? 001= 360K in 1.2M, ? 010= 1.2M in 1.2M, ? 011= 360K in 360K, ok 100= 360K in 1.2M, ok 101= 1.2M in 1.2M, ok 111= 720K in 720K, ok or 1.44M in 1.44M (state not used for 2.88) 043 Media state for diskette drive 1 dsk_media_st1 (see dsk_media_st0) 044 Starting state for drive 0 dsk_start_st0 045 Starting state for drive 1 dsk_start_st1 046 Current track number for drive 0 dsk_track_0 047 Current track number for drive 1 dsk_track_1 048 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ ADVANCED KEYBOARD DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Special keyboard type and mode keybd_flags_3 bit 7 Reading ID of keyboard 6 last char is 1st ID char 5 force num lock 4 101/102 key keyboard 3 right alt key down 2 right ctrl key down 1 E0h hidden code last 0 E1h hidden code last 049 Keyboard Flags (advanced keybd) keybd_flags_4 7 6 5 4 3 2 1 0 xmit char Resend Ack \ / error was ID Rec'd Rec'd LEDs 04A █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ REAL-TIME CLOCK & LAN DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Ptr offset to wait done flag @timer_wait_off 04B Ptr segment to wait done flag @timer_wait_seg 04C Timer low word, 1 microsecond clk timer_clk_low 04D Timer high word timer_clk_hi 04E Timer flag 00h = post acknowledgd timer_clk_flag 01h = busy 80h = posted 04F Local area network bytes (7) lan_1 050 unused 051 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ MORE ADVANCED VIDEO DATA █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Pointer to a save table of more @video_sav_tbl pointers for the video system SAVE TABLE offset type pointer to ────── ──── ──────────────────── 0 dd Video parameters 4 dd Parms save area 8 dd Alpha char set 0Ch dd Graphics char set 10h dd 2nd save ptr table 14h dd reserved (0:0) 18h dd reserved (0:0) 2ND SAVE TABLE (from ptr above) offset type functions & pointers ────── ──── ──────────────────── 0 dw Bytes in this table 2 dd Combination code tbl 6 dd 2nd alpha char set 0Ah dd user palette tbl 0Eh dd reserved (0:0) 12h dd reserved (0:0) 16h dd reserved (0:0) 052 unused 053 unused 054 unused 055 unused 056 Days since 1-Jan-1980 counter 057 Print screen status prn_scrn_stat 00h = Print screen ready 01h = Print screen in progress FFh = Error occurred 058 unused 059 unused 05A unused 05B unused 05C unused 05D █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ Floppy Disk Parameters █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ hi nibble = stepping rate in ms lo nibble = head unload time, ms 05E 2nd info byte bit 0 = 0 for DMA 05F Delay after use for motor off 060 Bytes per sector (2 = 512 bytes) 061 Number of sectors per track 9 = 360K/720K 0Fh = 1.2M 12h = 1.44M 24h = 2.88M 062 Gap Length 063 Data Length (0FFh=unused) 064 Format Gap Length 065 Format write byte 066 Head load time, in milliseconds 067 Motor startup wait time * .125ms 068 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ Video Hardware Registers █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ mode CGA 40 columns x 25 lines 069 mode CGA 80 columns x 25 lines 06A mode CGA graphics 06B mode MDA 80 columns x 25 lines 06C Video buffer bytes CGA 40x25 06D Video buffer bytes CGA 80x25 06E Video buffer bytes CGA Graphics 06F Video buffer bytes CGA Graphics 070 Video columns per modes 0-7 071 Video hardware modes (0-7) 072 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ dsk_info_table █ Hard Disk Information Tables █ █ █ █ Each sub-table contains a █ █ a set of 16 bytes for each █ █ particular disk type. █ █ █ █ Type number specified may █ █ differ with manufactures █ █ specification. The hard █ █ disk table shown here █ █ assumes the first entry █ █ is type 0. █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Number of cylinders, hdsk_type_0 073 Number of heads 074 Low write current cyl begin * 075 Write pre-compensation cylinder 076 Error correction burst length * 077 Miscellaneous bit functions: bits 0-2 disk option, XT only* 0-2 unused, all others 3 = 1 if > 8 heads 4 unused 5 = 1 for bad map at last cylinder + 1 6 or 7 = 1 no retries 078 Normal timeout * 079 Format timeout * 07A Check timeout * 07B Parking cylinder number 07C Number of sectors per track 07D Unused * indicates XT machines only 07E Unused 07F Video characters in graphic modes video_char_table 080 Characters, EGA 8x14 font 081 Characters, EGA 8x8 font (0-7F) 082 Characters, EGA 8x8 font (80-FF) 083 Character changes, EGA 8x14 font 084 Characters, VGA 8x16 font 085 Character changes, VGA 9x16 font 086 Video VGA parameter table ptr 087 Initial interrupt vectors int_vec_table 088 BIOS version date code rom_versn_date 089 Model FFh = PC model_type FEh = 1st XT FBh = later XTs FCh = AT type (286 & later) FAh = models 25/30 F9h = IBM lap-tops F8h = models 70/80 (80386) 08A Extended BIOS data (PS/2)or printer 4 BIOS_data_seg Printer 4 (PC,XT,AT & compatibles) 08B █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ VGA_parm_tbl █ Video VGA Parameter Tables █ █ █ █ 64 byte sub-table per mode █ █ offset/size function █ █ -- -------- -------------- █ █ 0 1 byte # of columns █ █ 1 1 byte # of rows █ █ 2 1 byte # bytes/char █ █ 3 1 word # bytes/page █ █ 5 5 bytes sequencer regs █ █ 10 25 bytes display regs █ █ 35 20 bytes attribute regs █ █ 55 9 bytes graphics regs █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ 08C █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ baud_rate_tbl █ Baud Rate Table █ █ █ █ Table of hex divisors for █ █ the serial ports. Table █ █ divisors for bauds 110 to █ █ 9600, and 19,200 on some. █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ 110 Baud rate divisor 08D █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ Config_tbl_size █ System Configuration Table █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Size of table in bytes 08E Model type 0F8h = PS/2 model 70-80 types 0FCh = PS/2 model 50-60 types also most 80286-80486 & Pentium compatibles 0FAh = 8088/86 model 25-30 type 08F Sub-Model type 090 BIOS revision number 091 Feature information bit 7=1, hard disk uses DMA 3 bit 6=1, dual interrupt chips bit 5=1, has real-time-clock bit 4=1, int 15h, ah=4Fh is supported (keyboard) bit 3=1, external wait support bit 2=1, has extended BIOS RAM bit 1=1, micro-channel bit 0=1, unused 092 Information bytes (future use) 093 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ Interrupt Vectors █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Divide error 094 Single Step 095 NMI 096 Debug 097 Overflow 098 Print Screen 099 Timer Ticks 09A Keyboard 09B Serial 09C Serial 09D Disk 09E Diskette 09F Bad Interrupt 0A0 Video 0A1 Equipment 0A2 Memory Size 0A3 Disk Services 0A4 General Services 0A5 ROM Basic 0A6 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ ROM BEGINNING █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ ROM signature word 0A7 Number of 512 byte pages 0A8 unused 0A9 █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ FONT - 8 wide, 14 high █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Video character font 0AA █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ FONT - 8 wide, 8 high █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Video characters 0-127 0AB █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ FONT - 8 wide, 8 high █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Video characters 128-255 0AC █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ FONT - 9 wide, 14 high █ █ █ █ First byte indicates the █ █ character to replace █ █ Followed by 14 bytes of data █ █ (the 9th bit is provided █ █ by the EGA/VGA adapter █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Video character font 0AD █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ FONT - 8 wide, 16 high █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Video character font 0AE █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ FONT - 9 wide, 16 high █ █ █ █ First byte indicates the █ █ character to replace █ █ Followed by 16 bytes of data █ █ (the 9th bit is provided █ █ by the EGA/VGA adapter █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Video character font 0AF █▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█ █ VIDEO MODE TABLES █ █ █ █ Note: The following structure █ █ is based on most EGA/ █ █ VGA adapters. Since █ █ they are used only █ █ internally the table █ █ may not follow the █ █ standard shown. █ █ █ █ EGA Cards - Mode order █ █ 0-0Fh, 10h normal █ █ 0Fh, 10h 16K RAM EGA █ █ 0-3, high res emulate █ █ VGA Cards - Mode order █ █ 0-Fh, 10-13h normal █ █ 0-3, high res emulate █ █ █ █ THIS IS A GUIDELINE AND MAY █ █ VARY DEPENDING ON THE CARD █ █▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█ Number of columns on display 0B0 Number of rows on display 0B1 Pixels per character 0B2 Bytes per page 0B3 Sequencer register values 0B4 Miscellaneous register value 0B5 CRT controller register values 0B6 Attribute register values 0B7 Graphics register values 0B8 System boot 0B9 Key Scan-Code Translate Table end :::::::::::::::::::::::::::::: LOCATION REMARKS :::::::::::::::::::::::::::::: ----------------------- Location Reference Remarks ------------------------ 01 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 1 ▒▒▒▒▒▒▒ SINGLE STEP 02 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 2 ▒▒▒▒▒▒▒ NON-MASKABLE HARDWARE INTERRUPT This function is called in the event of a memory parity error or may occur in the event of other hardware problems or failures (depends on the specific manufacturer's hardware). Displays the appropriate error message and halts the processor. 03 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 3 ▒▒▒▒▒▒▒ DEBUG BREAKPOINT 04 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 4 ▒▒▒▒▒▒▒ OVERFLOW 05 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 5 ▒▒▒▒▒▒▒ PRINT SCREEN Send the present active display screen contents to the printer if the printer is idle and not out of paper. The status of the print screen function is in prn_screen_stat at 0050:0000. Control-Break will terminate an active print screen operation. 06 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 6 ▒▒▒▒▒▒▒ BAD OPCODE DETECTED 07 08 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 8 ▒▒▒▒▒▒▒ TIMER TICKS (called by hardware 8259-1, IRQ 0) This is the primary timer used to control the clock and other key system resources. It is called indirectly by channel A of the 8253 timer every 18.2 milliseconds. Every timer tick also calls int 1Ch for user needs (int 1Ch points to an iret instruction unless changed by a resident program). The timer interrupt is given the highest maskable interrupt priority upon power up. The main timing functions of int 8 include increment of a 32-bit time since powered on counter, timer_hi and timer_low, and after 24 hours since powered on, timer_rolled is incremented. The last task of int 8 is turning off the floppy drive motor after 2 seconds of non-use. The counter dsk_motor_tmr is decremented upon each occurrence of int 8. When the count reaches zero, the motor is set off, and the motor running flags are cleared in dsk_motor_stat. 09 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 9 ▒▒▒▒▒▒▒ KEYBOARD I/O (called by hardware 8259-1, IRQ 1) When any key is pressed on the keyboard, the hardware calls this interrupt to service the pressed key or key combination. The hardware provides the key pressed in a non-ASCII scan code format read at i/o port 60h. The servicer acknowledges receipt of the key by toggling bit 7 of port 61h. (Port 61h should be read first, then bit 7 ored on, output to port 61h, then anded off, and resent to port 61h). The read key is decoded to yield an ASCII character, special function key (such as F1) or a control function like Left Shift Key down. The converted ASCII character is placed into the next available position in the circular queue keybd_queue to keybd_q_end. It is put in the position indicated by keydb_q_tail when it will not cause the loss of earlier entered data. The value keybd_q_head points to the oldest key pressed in the buffer which has not been removed from the queue (the normal process uses int 16h to remove keys from the queue and return the key value to the int 16h caller). The 16 word queue holds up to 16 keys. If keybd_q_head equals the keybd_q_tail, the queue is empty. Valid keys in the queue comprise the upper byte scan code and the lower byte ASCII character. If the key pressed has no ASCII equivalent (i.e F1 to F12), the lower byte is zero. Toggle and shift keys are not placed in the buffer, but appear in 2 status registers keybd_flags_1 and keybd_flags_2. Special key combinations will cause other events to occur: Ctrl-Alt_Del - Reset computer by jumping to power_on_reset Print screen - Call int_5_prn_scrn to print the current screen Ctrl-Break - Call int_1Bh control break key processor (DOS) Pause - Wait until an ASCII key is pressed, without placing the key in the queue Ctrl-Num Lock - Wait until an ASCII key is pressed, without placing the key in the queue Ctrl-Prt Scn - Toggle keyboard echo to printer Sys Req - Issue an interrupt 15h, ax=8500h when pressed, and interrupt 15h, ax=8501h when released Alt-Keypad - Convert decimal and insert into the BIOS keyboard buffer Shift keys - Save the new shift state (Ctrl, Alt, Shift, Insert, Caps Lock, Num Lock, Scroll Lock) 0A ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 0Ah ▒▒▒▒▒ General Adapter Use (called by hardware 8259-1, IRQ 2 - see below) On systems equipped with 2 interrupt controller chips (8259), IRQ 2 is used to support the second interrupt controller. In this case, int 71h (IRQ 9) is used to replace IRQ 2. Hardware calls to int 71h are redirected to this interrupt to maintain compatibility. 0B ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 0Bh ▒▒▒▒▒ RS-232 SERIAL HANDLER (called by hardware 8259-1, IRQ 3) Called by the secondary serial port chip. 0C ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 0Ch ▒▒▒▒▒ RS-232 SERIAL HANDLER (called by hardware 8259-1, IRQ 4) Called by the primary serial port chip. 0D ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 0Dh ▒▒▒▒▒ XT HARD DISK CONTROLLER (called by hardware 8259-1, IRQ 5) 0E ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 0Eh ▒▒▒▒▒ FLOPPY DISK CONTROLLER (called by hardware 8259-1, IRQ 6) 0F ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 0Fh ▒▒▒▒▒ PRINTER CONTROLLER (called by hardware 8259-1, IRQ 7) This interrupt is normally avoided. If a bad interrupt occurs, it will vector to this spot (when caused by a misprogrammed 8259 interrupt controller) 10 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 10h ▒▒▒▒▒ VIDEO DISPLAY SERVICES Called with: ah = primary function number Returns: (unless otherwise indicated) ax - altered (some systems may not alter ax) Functions: ah = 0 Set video display mode in al. ah = 1 Set cursor size Call with: ch = top line, 0-32 cl = bottom line, 0-32 ah = 2 Set cursor location Call with: bh = page number, 0 = 1st page dh = row (0 for top row) dl = column (0 for leftmost) ah = 3 Get cursor location Call with: bh = page number, 0 = 1st page Returns: ch/cl = cursor size (top & bottom) dh/dl = row and column of cursor ah = 4 Get light pen location Returns: ah = 0 not on/unsupported & bx,cx,dx changed 1 status valid bx = pixel column cx = horizontal line number dh/dl = row and column ah = 5 Set Page number al, 0 = 1st page ah = 6 Up scroll screen Call with: al = # bottom lines to clear, set 0 for all bh = attribute to fill cleared lines ch/cl = row/column of top left scroll corner dh/dl = row/column of bottom right scroll corner ah = 7 Down scroll screen Call with: al = # top lines to clear, set 0 for all bh = attribute to fill cleared lines ch/cl = row/column of top left scroll corner dh/dl = row/column of bottom right scroll corner ah = 8 Get character & attribute at cursor Call with: bh = page number, 0 = 1st page Returns: ah/al = attribute/character ah = 9 Write character & attribute at cursor (graphics modes) Call with: al = character bh = page number, 0 = 1st page bl = attribute, bit 7 = 1 to xor with old color cx = Number of same characters to write ah = 0Ah Write character at cursor (graphics modes) Call with: al = character bh = page number, 0 = 1st page cx = Number of same characters to write ah = 0Bh Set colors (typically in low res modes) Call with: bh = 0, bl = color low res background, border bh = 1, bl = 0/1 for low res color group 0/1 ah = 0Ch Write graphics dot Call with: al = color, bit 7 = 1 to xor bit with old color cx/dx = pixel row/pixel column ah = 0Dh Read graphics dot Call with: cx/dx = pixel row/pixel column ah = 0Eh Write in ASCII mode (cr, lf, bell, and bs as operators) Call with: al/bl = character/color ah = 0Fh Get video info Returns: ah = columns active al = active video mode bh = active page, 0 = 1st page ah = 10h Colors (EGA/VGA) Called with al = subfunction al = 1 bl = color register (0-15) bh = color to set al = 2 es:dx = ptr to change all 16 colors & overscan # al = 3 bl = color high bit as: 0-intensity, 1-blink For VGA equipped systems only al = 7 bl = color register to get in bh al = 8 bh = returned overscan value al = 9 es:dx = ptr where to put all 16 colors & overscan al = 10h bx = color register to set; ch/cl/dl = grn/blu/red al = 12h es:dx = ptr to change color registers bx = 1st register to set, cx = # of registers al = 13h bl = 0, set color page mode in bh bl = 1, set page; bh = page number al = 15h bx = color reg to read; ch/cl/dl = grn/blu/red al = 17h es:dx = ptr where to load color regs bx = 1st register to get, cx = # of registers al = 1Ah get color page info; bl = mode; bh = page # ah = 11h Reset mode with new character set (leave memory as-is) al = 0 Character set load es:bp = ptr to table of chars bl/bh = which block/bytes per char cx/dx = # of characters/where to start in block al = 1 bl = block to load the mono character set al = 2 bl = block to load the double wide character set al = 3 bl = block select related to attribute al = 4 bl = block to load the 8 by 16 set (VGA) al = 10h - 14h same as 0 - 4, must occur after setting mode al = 20h es:bp = ptr to table of char, using int 1Fh ptr al = 21h es:bp = ptr to table of char, using int 43h ptr bl = 0-dl=# rows; 1-14 rows; 2-25 rows; 3-43 rows cx = number of bytes per character in table al = 22h use 8 by 14 char set, bl=rows (see al=21h) al = 23h use double wide char set, bl=rows (see al=21h) al = 24h use 8 by 16 char set, bl=rows (see al=21h) Get table pointer and info al = 30h es:bp = ptr returned; cx=bytes per char; dl=rows bh = 0, get int 1Fh bh = 4, get double wide bh = 1, get int 43h bh = 5, get mono 9 by 14 bh = 2, get 8 by 14 bh = 6, get 8 by 16 (VGA) bh = 3, get double wide bh = 7, get 9 by 16 (VGA) ah = 12h Miscellaneous functions, bl = sub-function bl = 10h Get info, bh = 0-now color, 1-now mono ch/cl = info bits/switches bl = 20h Set print screen to work with EGA/VGA Functions for VGA only (bl = 30-34h return al = 12h) bl = 30h Set # of scan lines, 0-200, 1-350, 2-400 activates after mode change bl = 31h ax = 0/1 allow/prevent palette load with new mode bl = 32h al = 0/1 video off/on bl = 33h al = 0/1 gray scale summing off/on bl = 34h al = 0/1 scale cursor size to font off/on bl = 35h switch between adapter and motherboard video al = 0, adapter off, es:dx = save state area al = 1, motherboard on al = 2, active video off, es:dx = save area al = 3, inactive video on, es:dx = save area bl = 36h al = 0/1 screen off/on ah = 13h Write character string (cr, lf, bell, and bs as operators) Call with: al = 0/1 write characters, cursor not/is moved bl = attribute of all characters = 2/3 write characters, cursor not/is moved string alternates character & attribute bh = page number, 0 = 1st page cx = number of characters dh/dl = row and column to start es:bp = ptr to character string ah = 14h LCD display support, al = sub-function al = 0, es:di = ptr to font table to load bl/bh = which block/bytes per char cx/dx = # of characters/where to start in block al = 1, bl = block # of ROM font to load al = 2, bl = how to support high intensity ah = 15h LCD info table ptr returned in es:di ax = 0 there is no alternate adapter ax = 5140h LCD is the alternate ax = 5153h CGA is alternate ax = 5151h MDA is alternate **** VGA SUPPORT ONLY **** ah = 1Ah Get/Set types of displays which are operating al = 0, get displays, returns al = 1Ah bl = in use display code bh = alternate display code al = 1, set codes, returns al = 1Ah bl = in use display code bh = alternate display code codes: 0 = no display 1 = mono display 2 = CGA 4 = EGA, color 5 = EGA, mono 6 = PGA 7 = VGA, mono (PS/2 MCA only) 8 = VGA, color (PS/2 MCA only) Bh = VGA, mono (PS/2 non MCA) Ch = VGA, color (PS/2 non MCA) FFh = display type not known ah = 1Bh Get video system information call with: bx = 0 es:di = ptr to buffer where to put info ah = 1Ch Video system save & restore, al = sub-function call with: al = 0, get buffer size = 1, save system, buffer at es:bx = 2, restore system, buffer at es:bx cx bit 0 = 1 for hardware registers bit 1 = 1 for software states bit 2 = 1 for colors & DAC registers 11 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 11h ▒▒▒▒▒ EQUIPMENT INSTALLED Returns: ax = equip_install word 15 14 13 12 11 10 9 8 \ / game \ / # of printer port # of RS-232 ports 0-3 used ports 0-4 7 6 5 4 3 2 1 0 \ / \ / \ / Math | # of video mode RAM uP no floppy at boot up 00=16K floppy drives 00=EGA 01=32K drive 1-4 01=CGA-40 10=48K if 0 if bit 10=CGA-80 11=64K 0 = 1 11=MDA-80 (old PCs) Note: bit 13 = modem on some PC lap-tops bit 2 = mouse on MCA and some others Regs used: ax 12 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 12h ▒▒▒▒▒ SYSTEM MEMORY SIZE Returns: ax = number of contiguous 1K bytes blocks of memory from 0 to 640 K. Regs used: ax 13 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 13h ▒▒▒▒▒ FLOPPY DISK SERVICES Note: Floppy disk services may be vectored to this routine from int 40h on newer systems with hard disk support inside the BIOS. Call with: ah = sub-function number dl = drive number (unless otherwise noted), drive a: = 0 Returns: carry = 0 if function ok ah = status (unless otherwise noted) ah = 0 Function ok ah = 1 Invalid value passed or unsupported function ah = 2 Can not locate address mark ah = 3 Floppy write protected ah = 4 Sector not found ah = 6 Floppy changed line on (1.2 meg drives) ah = 8 DMA overrun occurred ah = 9 DMA attempted across 64K byte boundary ah = 0Ch Media type not found ah = 10h CRC read error ah = 20h Floppy controller failure ah = 40h Seek operation failed ah = 80h Floppy drive not ready Functions: ah = 0 Floppy disk controller reset ah = 1 Get last status ah = 2 Read sectors Call with: al = number of sectors to read ch/cl = starting track/starting sector dh = head number, head 0 = 0 es:bx = ptr to buffer where to put data ah = 3 Write sectors Call with: al = number of sectors to write ch/cl = starting track/starting sector dh = head number, head 0 = 0 es:bx = ptr to buffer where to get data Return: al = number of sectors written ah = 4 Verify sectors Call with: al = number of sectors to compare ch/cl = starting track/starting sector dh = head number, head 0 = 0 es:bx = ptr to buffer where to compare data Return: al = number of sectors checked ah = 5 Format track Call with: al = number of sectors to format ch/cl = starting track/starting sector dh = head number, head 0 = 0 es:bx = ptr to table of address fields ah = 8 Get drive information (not supported by all systems) Returns: ax/bh = 0 size dia. size dia. bl = drive type: 1=360K 5.25 3=720K 3.5 2=1.2M 5.25 4=1.4M 3.5 cx bits 7&6, 15-8 = number of tracks, 0=1 track bits 5-0 = number of sectors per track dh/dl = # of heads/number of floppy drives es:di = ptr to floppy parameter table ah = 15h Get drive type (not supported by all systems) Returns: ah = 0 no drive ah = 1/2 floppy changed line not/is available ah = 16h Get changed floppy status (not supported by all systems) Returns: ah = 0 floppy in drive, carry = 0 ah = 1 bad drive number, carry = 1 ah = 6 floppy out of drive, carry = 1 ah = 80h drive not ready, carry = 1 ah = 17h Specify media type for a drive Call with: al = 1 use a 320/360K floppy in 360k drive al = 2 use a 360K floppy in a 1.2M drive al = 3 use a 1.2M floppy in a 1.2M drive al = 4 use a 720K disk in a 720K drive ah = 18h Prepare for format (not supported by all systems) Call with: cx bits 7&6, 15-8 = number of tracks, 0=1 track bits 5-0 = number of sectors per track Returns: es:di = ptr to floppy parameter table 14 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 14h ▒▒▒▒▒ RS-232 SERIAL PORTS SERVICES Call with: ah = sub-function number dx = communications number, com1 = 0 Returns: ah = line status, bit 0 = Data ready bit 1 = Overrun error bit 2 = Parity error bit 3 = CRC framing error bit 4 = Break detect bit 5 = Xmit buffer register empty bit 6 = Xmit shift out register empty bit 7 = No response, ignore bits 0-6 al = modem status, bit 0 = Change in Clear To Send bit 1 = Change in Data Set Ready bit 2 = Falling edge ring detect bit 3 = Change in receive detect line bit 4 = Clear to Send (CTS) bit 5 = Data Set Ready (DTS) bit 6 = Ring detected bit 7 = Receive detect line Functions: ah = 0 Reset the specified port Call with: al serial port register values bits 7 6 5 4 3 2 1 0 --baud-rate-- -Parity- Stop --Word-- 000 = 110 bits bit size 001 = 150 (bits) 010 = 300 00 = off 0=1 011 = 600 01 = odd 1=2 10 = 7 100 = 1200 10 = off 11 = 8 101 = 2400 11 = even 110 = 4800 111 = 9600 ah = 1 Transmit a character Call with: al = character to send (not changed on exit) ah = 2 Received a character Returns: al = character received ah = 3 Get status ah = 4 Advanced Initialization (not supported on all systems) Call with: al = 0/1 no break/break bh = Parity, 0 = none 3 = stick odd 1 = odd 4 = stick even 2 = even bl = 0/1 Stop bits set to 1/2 ch = Word size, 0 = 5 bits 2 = 7 bits 1 = 6 bits 3 = 8 bits cl = Baud rate, 0 = 110 5 = 2400 1 = 150 6 = 4800 2 = 300 7 = 9600 3 = 600 8 = 19200 4 = 1200 ah = 5 Advanced port control (not supported on all systems) al = 0 Get modem register Returns: bl bit 0 = Data Terminal Ready (DTR) bit 1 = Request To Send (RTS) bit 2 = Out 1 bit 3 = Out 2 bit 4 = Loop modem al = 1 Set modem register Call with: bl = value for register (see above) 15 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 15h ▒▒▒▒▒ GENERAL SERVICES On old PCs this function is only used for cassette servicing. Additional functions have been added for advanced features with newer equipment. Called with: ah = function code Returns: CF = 0 if successful CF = 1 if failure or function not supported Functions: ah = 0 Cassette motor set on ah = 1 Cassette motor set off ah = 2 Read cx bytes from cassette, es:bx = ptr to load area ah = 3 Write cx bytes to cassette, es:bx = ptr to read area ah = 0Fh Disk format hook, called from disk format routines after a cylinder access completed. Called with: al = 1-undergoing surface analysis, 2-if formatting ah = 21h Error log (PS 2), al = 0 to read, al = 1 to write *** LAPTOP MACHINES ONLY - 40h to 44h *** ah = 40h Systems info in cx, bx - al = 0 to read, 1 to write for modem info in bx - al = 2 to read, 3 to write ah = 41h Wait for an event, dx = i/o port to read or use es:di as ptr to user event. al = type of event 0-4,11-14 bh = event mask, bl = # of 55ms counts to timeout ah = 42h Power off, al = 0 or 1 for mode of power off ah = 43h Get system status in al 7 6 5 4 3 2 1 0 low extrn bad pwr up modem ports LCD battery pwr time alarm on on missing ah = 44h Modem power, al = 0 turn off, al = 1 turn on *** FUNCTIONS IN RECENT BIOS VERSIONS ONLY *** ah = 4Fh Keyboard input hook, called every keystroke with al = scan code. CF = 1 to change or use the scan code in al. CF = 0 to ignore the key. ah = 80h Open device number bx, in process number cx. ah = 81h Close device number bx, in process number cx. ah = 82h Terminate device number bx ah = 83h Wait for timeout, and set bit 15 at ptr es:bx when timed out. al = 0 to set wait period cx:dx uSec, al = 1 to stop timeout timer. ah = 84h Game port read, dx = 0 to read switches into al high nibble, dx = 1 to read linear position (Unit 1: ax = x, bx = y Unit 2: cx = x, dx = y) ah = 85h Get system request key state, al = 0 down, al = 1 up ah = 86h Wait cx:dx microseconds before return ah = 87h Transfer cx words to/from memory above 1 meg es:si ptr to table with source & destination ptrs: es:si -> zeros db 16 dup(0) src_seg_limit dw ? ; 1-64K bytes scr_ptr_low dw ? ; 0-64K range scr_ptr_high db ? ; 0-16 Meg range scr_rights db 93h ; r/w access scr_zero dw 0 dst_seg_limit dw ? ; 1-64K bytes dst_ptr_low dw ? ; 0-64K range dst_ptr_high db ? ; 0-16 Meg range dst_rights db 93h ; r/w access dst_zero dw 0 zeros2 db 16dup(0) Notes: cx = 32K words max xfer, ptr_low & ptr_high form a 24 bit physical address (do not use a segment) Return codes: al = 0 if ok, al = 1 parity error al = 2 other errors, al = 3 gate addr line 20 bad ah = 88h Get extended memory size (above 1 Meg boundary) ax = (number of bytes / 1024) ah = 89h Go to protected mode of operation. es:si ptr to table comprised of 8 groups of 8 byte ptr sub-arrays. Each. group is formed from 8 bytes as follows: seg_limit dw ? ; 1-64K bytes ptr_low dw ? ; 0-64K range ptr_high db ? ; 0-16 Meg range rights db 93h ; read/write access zero dw 0 ; set to zero Ptr_low & high form a 24 bit physical address. The 8 groups are as follows: es:si -> Group_1 Set to all zero Group_2 ptr to beginning of Group_1 Group_3 ptr to Interrupt Descript Table IDT Group_4 ptr to present DS segment Group_5 ptr to present ES segment Group_6 ptr to present SS segment Group_7 ptr to present CS segment Group_8 ptr where to jump to when done Also: bh & bl set as offset from beginning of IDT to spot where 1st & 2nd set of 8 hardware interrupts begin. Returns ah = 0 if ok, regs changed: ax,bp,ds,es,ss,cs ah = 90h Device busy - used to signal DOS when it must wait. Type 0 Disk timeout 0FCh Hard disk timeout codes 1 Floppy timeout (PS 2 only) (al) 2 Keyboard no timeout 0FDh Floppy motor timeout 3 Mouse timeout 0FEh Printer timeout 80h Local area network (es:bx = network cntrl block Returns CF = 0 if failure, 1 if minimum wait time occurred ah = 91h Interrupt done - used to signal DOS when hardware done al = type code (Device busy type codes) ah = C0h Get ROM system information table ptr in es:bx. See data area starting at byte "sys_info_size". *** PS 2 & COMPATIBLES ONLY - C1h to C4h *** ah = C1h Get Extended BIOS data area segment in es ah = C2h Mouse support (BIOS). Sub-function code in al al = 0 if bh = 0 mouse off, bh = 1 mouse on al = 1 reset mouse & parameters, returns bh = 0 bl altered on return al = 2 Set number of updates per second in bh, bh = 0 - 10 updates/sec 4 - 80 updates/sec 1 - 20 updates/sec 5 - 100 updates/sec 2 - 40 updates/sec 6 - 200 updates/sec 3 - 60 updates/sec al = 3 Set resolution in counts per millimeter: bh = 0 - 1 cnts per mm 2 - 4 cnts per mm 1 - 2 cnts per mm 3 - 8 cnts per mm al = 4 Get device type, bh = 0 al = 5 Initialize pointing device interface data size bh = size 1 to 8 (1 to 8 bytes) al = 6 Additional sub-functions in bh: bh = 0 Get status, cl = cnts per mm (see al=3) dl = updates/sec in hex, bl = status: bit 6 = mode (0=stream, 1=remote) 5 = 0 disabled, 1 enabled 4 = scaling (0=1:1, 1=2:1) 2 = Left button pressed 0 = right button pressed bh = 1 Set scaling to 1:1 bh = 2 Set scaling to 2:1 al = 7 Set location to "call far" when data available in es:bx Return code for all sub-functions in al: al = 0 successful 3 interface error 1 bad function call 4 resend 2 invalid input 5 no far call installed ah = C3h Watchdog timer mode al = 0 disable, al = 1 enable, bx = set counter value 1 to FFh ah = C4h Bus option select (POS) subfunction in al, al = 0 Get base POS adapter register address in dx 1 Enable setup for slot bl 2 Adapter enable 16 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 16h ▒▒▒▒▒ KEYBOARD SERVICES Call with: ah = sub-function number Functions: ah = 0 Get a key, and wait until one is available if none are in the queue. Returns: ah = keyboard scan code al = ASCII character, or 0 if non-ASCII ah = 1 Get key status Returns: zero flag = 0 if a valid key is in the queue ah = keyboard scan code al = ASCII character, or 0 if non-ASCII zero flag = 1 if no keys in the queue ah = 2 Get shift status register Returns: al = bits 7 6 5 4 3 2 1 0 right left ctrl alt scrl num cap insrt -------shifts------ ------toggles------- 1 = down 1 = on ah = 3 Set repeating character rate (not supported in all systems) Call with: al = 5 bh = start delay, 0 = 250 ms 2 = 750 ms 1 = 500 ms 3 = 1000 ms bl = speed in characters per second - values range from 0 = 30 cps, to 1Fh = 2 cps ah = 5 Load keyboard queue (not supported in all systems) Call with: ch/cl = scan code/character to load into the queue Returns: al = 0 if ok, 1 if keyboard queue is full **** Support for extended keyboard functions **** ah = 10h Get a key (similar to ah = 0, not supported in all systems) ah = 11h Get key status (similar to ah = 1, not supported in all systems) ah = 12h Get shift info (similar to ah = 2, not supported in all systems) 17 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 17h ▒▒▒▒▒ PRINTER SERVICES Call with: ah = function code dx = printer number 0-2 (some systems allow 0-3) Returns: ah = status bits 7 6 5 4 3 2 1 0 not acknow- no select I/O unused no busy ledge paper error response __________from printer__________ Functions: ah = 0 Send character to printer, al = character ah = 1 Printer port initialization ah = 2 Get printer status in ah 18 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 18h ▒▒▒▒▒ ROM BASIC 19 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 19h ▒▒▒▒▒ BOOTSTRAP LOADER Floppy drive a: attempts a read from the first sector of the disk. If read properly (i.e a boot disk is in drive a:), control is transferred to the loaded program. The boot sector at track 0, sector 1 is transferred to memory at 0:7C00h. dh = drive which was used (0=A:). Control is passed to 0:7C00h. 1A ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 1Ah ▒▒▒▒▒ REAL-TIME CLOCK SERVICES Call with: ah = sub-function number Functions: ah = 0 Get system timer (increments every 54.92 ms from int 8) Returns: al = # of 24 hour periods since read/powered up cx:dx = 32 bit count ah = 1 Get system timer & reset 24 hour counter Returns: cx:dx = 32 bit count This subfunction should NEVER be used by an application. It is intended for the operating system only. Use by an application running at midnight will cause the operating system clock to lose a day! **** System must have CMOS clock for services 2-0Bh **** ah = 2 Get time in BCD format Returns: ch/cl = hours/minutes dh = seconds dl = 0/1 if daylight savings time operation off/on carry flag = 0 if clock ok, 1 if stopped ah = 3 Set time in BCD format Call with: ch/cl = hours/minutes dh = seconds dl = 0/1 if daylight savings time operation off/on ah = 4 Get date in BCD format Returns: cx = four digit year dh/dl = month/day carry flag = 0 if clock ok, 1 if stopped ah = 5 Set date in BCD format Call with: cx = four digit year dh/dl = month/day ah = 6 Set 24 hour alarm (alarm vectors to int 4Ah) Call with: ch/cl = hours/minutes dh = seconds ah = 7 Clear alarm ah = 9 Get alarm time & status Returns: ch/cl = hours/minutes dh = seconds dl = 0/1 alarm off/on ah = 0Ah Get days counter Returns: cx = number of days since 1-Jan-80 ah = 0Bh Set days counter Call with: cx = number of days since 1-Jan-80 1B ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 1Bh ▒▒▒▒▒ KEYBOARD BREAK (when Control-Break pressed) 1C ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 1Ch ▒▒▒▒▒ TIMER TICKS - Called every 18.2 ms 1D ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 40h ▒▒▒▒▒ FLOPPY DISK SERVICES 1E ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 70h ▒▒▒▒▒ REAL-TIME CLOCK (called by hardware 8259-2, IRQ 8) This interrupt services the real-time clock hardware. The hardware supports 2 modes of operation, an interrupt at a specific 24 hour interval (i.e 9:42 am), or repeatedly every 0.976 ms (1,024 Khz). Both modes can operate at the same time if needed. In the 24 hour alarm mode, the interrupt is vectored here by hardware and interrupt 4Ah is called to alert the application program of the alarm. Int 4Ah is not handled by the BIOS other than to return, and is normally revectored by a particular application using the alarm. When repeating interrupt mode is active, the 32-bit microsecond counter consisting of timer_clk_low and timer_clk_hi is decremented by 976 us on every interrupt. When the timer reaches zero, the byte pointed to by the offset @timer_wait_off and segment @timer_wait_seg is set to 80h (this pointer is set by an application program through int 1Ah function ah=6). 1F ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 71h ▒▒▒▒▒ For General Adapter Use (called by hardware 8259-2, IRQ 9) The BIOS calls interrupt 0Ah to simulate IRQ 2, which is no longer available on AT+ systems. Since IRQ 9 is the same physical line as the IRQ 2 line on the PC, it is recommended an adapter use interrupt Ah to handle IRQ 9. This maintains full compatibility will all platforms. 20 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 72h ▒▒▒▒▒ For General Adapter Use (called by hardware 8259-2, IRQ 10) 21 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 73h ▒▒▒▒▒ For General Adapter Use (called by hardware 8259-2, IRQ 11) 22 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 74h ▒▒▒▒▒ For General Adapter Use (called by hardware 8259-2, IRQ 12) 23 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 75h ▒▒▒▒▒ MATH COPROCESSOR (called by hardware 8259-2 IRQ 13) The external math coprocessor invokes this interrupt. Int 75h calls the non-maskable interrupt int 2 to flag an error occurred with the current math operation. This is done to maintain full compatibility with the original PC/XT which had the coprocessor connected to interrupt 2 (NMI). In normal operation, the program using the math coprocessor is responsible for hooking interrupt 2h and handling the error. If it does not hook interrupt 2h, the BIOS will usually halt the system. 24 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 76h ▒▒▒▒▒ HARD DISK CONTROLLER (called by hardware 8259-2 IRQ 14) When the hard disk controller has completed its task, it signals completion though hardware activation of int 76h. The status in hdsk_int_flags is set to "done", a value of 0FFh. Interrupt 15, function 91h may also be called to signal the interrupt is done. 25 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 77h ▒▒▒▒▒ For General Adapter Use (called by hardware 8259-2 IRQ 15) 26 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 13h ▒▒▒▒▒ HARD DISK SERVICES Call with: ah = sub-function number dl = drive number (unless otherwise noted) 80h or 81h for fixed disk 0 or 1. Returns: carry = 0 if function ok ah = status (unless otherwise noted) ah = 0 Function ok ah = 1 Invalid value passed or unsupported function ah = 2 Can not locate address mark ah = 3 Write protected ah = 4 Sector not found ah = 5 Reset failure ah = 7 Parameter activity failed ah = 8 DMA overrun occurred ah = 9 DMA attempted across 64K byte boundary ah = 0Ah Sector flag bad ah = 0Bh Cylinder bad ah = 0Dh Wrong # of sectors (format) ah = 0Eh Detected control data address mark ah = 0Fh DMA arbitration level has invalid range ah = 10h CRC or EDC (Error Detect & Correct) has an unresolvable error ah = 11h Data corrected by EDC ah = 20h Disk controller failure ah = 40h Seek operation failed ah = 80h Hard disk not ready ah = BBh Error not defined ah = CCh Write error ah = E0h Error register is zero ah = FFh Disk sense error If dl bit 7 was set to 1 on entry: cx bits 7&6, 15-8 = highest cylinder number bits 0-5 = highest sector number dh = highest head number dl = number of hard disks (1 or 2) Functions: ah = 0 Hard disk controller reset ah = 1 Get last status ah = 2 Read sectors Call with: al = number of sectors to read cx bits 7&6, 15-8 = cylinder number bits 0-5 = sector number dh = head number, head 0 = 0 es:bx = ptr to buffer where to put data ah = 3 Write sectors Call with: al = number of sectors to write cx bits 7&6, 15-8 = cylinder number bits 0-5 = sector number dh = head number, head 0 = 0 es:bx = ptr to buffer where to get data ah = 4 Verify sectors Call with: al = number of sectors to compare cx bits 7&6, 15-8 = cylinder number bits 0-5 = sector number dh = head number, head 0 = 0 ah = 5 Format cylinder (non-ESDI type disks) Call with: cx bits 7&6, 15-8 = cylinder number dh = head number, head 0 = 0 es:bx = ptr to bad sector map (non XT) al = interleave number (XT only) ah = 6 Format cylinder & set bad sector flags (XT only) Call with: al = interleave number cx bits 7&6, 15-8 = cylinder number dh = head number, head 0 = 0 ah = 7 Format drive, begin at specific cylinder (XT only) Call with: al = interleave number cx bits 7&6, 15-8 = cylinder number dh = head number, head 0 = 0 ah = 8 Get drive parameters Returns: cx bits 7&6, 15-8 = max cylinder number bits 0-5 = max sector number dh = max head number, head 0 = 0 ah = 9 Set parameters for drive (ignored for ESDI drives) Call with dh = 80h to use int 41h ptr, drive 0 dh = 81h to use int 46h ptr, drive 1 ah = 0Ch Disk seek Call with: cx bits 7&6, 15-8 = cylinder number dh = head number, head 0 = 0 ah = 0Dh Secondary Disk Reset ah = 10h Check if drive is ready ah = 11h Recalibrate drive ah = 15h Get drive type (all but XT systems) Returns: ah = 0 no drive (cx & dx = 0) ah = 3 hard disk cx:dx = size of disk in 512 byte blocks al = 4 use a 720K disk in a 720K drive ah = 19h Park disk heads (PS/2 systems only) ah = 1Ah Format hard disk (ESDI only) Call with: al = number of blocks in defect table (0=none) cl bit 0 = 1 when no primary defect map bit 1 = 1 when no secondary defect map bit 2 = 1 allow logging found surface errors in the secondary defect map bit 3 = 1 Do extended surface analysis bit 4 = 1 interrupt after each cyldr format 27 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ unused ▒▒▒▒▒ Unused interrupt vector termination This routine processes invalid and unused interrupt requests. The hardware IRQ number is loaded into gen_int_occured, and the interrupt cleared. For software calls to an unused interrupt, a value 0FFh is loaded into gen_int_occured, and the routine returns to the caller without changing registers. Alternatively, some systems simply return (iret). 28 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ int 18h ▒▒▒▒▒ ROM BASIC Note: ROM basic points to F600 segment, and has been adjusted to segment F000 to process in-line with the balance of the BIOS code. Internal data references may shift to segment F600 depending on implementation. 29 ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ System Reset ▒▒▒▒▒ SYSTEM RESET Reset the computer system. General operation includes a test of of the CPU, ROM checksum, and initialization of hardware including: Memory system Timer/Counter (which is also used for RAM refresh) Interrupt Controller(s) DMA Controller(s) Keyboard Controller Video Controller & Video RAM Floppy Controller Hard Disk Controller (if present) Portions of the hardware may also have specific tests made to insure reliable operation. Test failures may display error code on the screen if the video subsystem is operational, or generate beeps or LED blinks to signify the error. Note: A soft reset uses the warm_boot_flag to skip the memory tests. (i.e. from pressing Ctrl-Alt-Del). The system checks for installed ROMs by searching memory from C000h to the beginning of the BIOS, in 2K chunks. ROM memory is identified if it starts with the word AA55h. It is followed a one byte field length of the ROM (divided by 512). If ROM is found, the BIOS will call the ROM at an offset of 3 from the beginning. This feature was not supported in the earliest PC machines. The last task turns control over to the bootstrap loader (assuming the floppy controller is operational) 2A ══════ BIOS EXTERNAL ENTRY POINT ═══════════════════════════════════════ 2B ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ BIOS Setup ▒▒▒▒▒▒▒ BIOS SETUP ROUTINES When a special key combination is pressed, this setup routine is run to allow changing CMOS BIOS values. Typical key combinations include CTRL-ALT-ESC, CTRL-ALT-S, or others to start the setup. Once invoked, it may issue a system reset to let other application software, other BIOS routines, and TSR's to configure the system with the new information. Typical options include: Present time and date Floppy disk settings Hard disk table selection Video display Memory size Speed of clock and/or bus 2C ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ INTERRUPT ▒▒▒▒▒ 2D ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ BIOS Initialization ▒▒▒▒▒▒▒ This portion is called when the main computer BIOS passes control to allow this BIOS to perform it's one-time start up code. 2E ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ Exception Handler ▒▒▒▒▒ Protected Mode Exception Handler When the BIOS goes into protected mode, the exception vectors will point to this handler. The usual process is to initiate a system reset, since no interrupts should occur during this process. end ::::::::::::::::::::::::::::: SUBROUTINE REMARKS ::::::::::::::::::::::::::::: ---------------------- Subroutine Reference Remarks ----------------------- end NOTES: 1) Entries must be in consecutive sequential order. 2) Remark characters ";" are automatically inserted. 3) Up to 64,000 characters per remark, 32M maximum file size.