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back2root:ibm-pc-ms-dos:hardware:informations:bios_data_area
Table des matières
Ceci est une ancienne révision du document !
BDA - BIOS Data Area - PC Memory Map - WIP
Bios Memory Maps
| Address | Size | Description |
|---|---|---|
| 00:00 | 256 dwords | Interrupt vector table |
| 30:00 | 256 bytes | Stack area used during post and bootstrap |
| 40:00 | word | COM1 port address |
| 40:02 | word | COM2 port address |
| 40:04 | word | COM3 port address |
| 40:06 | word | COM4 port address |
| 40:08 | word | LPT1 port address |
| 40:0A | word | LPT2 port address |
| 40:0C | word | LPT3 port address |
| 40:0E | word | LPT4 port address (except PS/2) Extended BIOS Data Area segment (PS/2, see EBDA) |
| 40:10 | 2 bytes | Equipment list flags (see INT 11 - below) |
| 40:12 | byte | PCjr: infrared keyboard link error count |
| 40:13 | word | Memory size in Kbytes (see INT 12) |
| 40:15 | byte | Reserved |
| 40:16 | byte | PS/2 BIOS control flags |
| 40:17 | byte | Keyboard flag byte 0 (see KB FLAGS - below) |
| 40:18 | byte | Keyboard flag byte 1 (see KB FLAGS - below) |
| 40:19 | byte | Storage for alternate keypad entry |
| 40:1A | word | Offset from 40:00 to keyboard buffer head |
| 40:1C | word | Offset from 40:00 to keyboard buffer tail |
Details
0040:0010 - INT 11 registers
| bit | 40:10 (value in INT 11 register AL) |
|---|---|
| 0 | IPL diskette installed |
| 1 | math coprocessor |
| 2-3 | old PC system board RAM < 256K PS/2 bit 2: pointing device installed; bit 3 :not used |
| 4-5 | initial video mode |
| 6-7 | # of diskette drives, less 1 |
| bit | 40:11 (value in INT 11 register AH) |
|---|---|
| 0 | 0 if DMA installed |
| 1-3 | number of serial ports |
| 4 | game adapter |
| 5 | not used, internal modem (PS/2) |
| 6-7 | number of printer ports |
0040:0017 - Keyboard flag 0
| bit | description |
|---|---|
| 0 | right shift key depressed |
| 1 | left shift key depressed |
| 2 | CTRL key depressed |
| 3 | ALT key depressed |
| 4 | scroll-lock is active |
| 5 | num-lock is active |
| 6 | caps-lock is active |
| 7 | insert is active |
0040:0018 - Keyboard flag 1
| bit | description |
|---|---|
| 0 | left CTRL key depressed |
| 1 | left ALT key depressed |
| 2 | system key depressed and held |
| 3 | suspend key has been toggled |
| 4 | scroll lock key is depressed |
| 5 | num-lock key is depressed |
| 6 | caps-lock key is depressed |
| 7 | insert key is depressed |
Floppy/drive Information Table
| Address | Size | Description |
|---|---|---|
| 40:1E | 32 bytes | Keyboard buffer (circular queue buffer) |
| 40:3E | byte | Drive recalibration status (see below) |
| 40:3F | byte | Diskette motor status (see below) |
| 40:40 | byte | Motor shutoff counter (decremented by INT 8) |
| 40:41 | byte | Status of last diskette operation (see INT 13,1 - below) |
| 40:42 | 7 bytes | NEC diskette controller status (see FDC) |
Details
0040:003e - Drive Recalibration status
| bit | description |
|---|---|
| 0 | 1=recalibrate drive 0 |
| 1 | 1=recalibrate drive 1 |
| 2 | 1=recalibrate drive 2 |
| 3 | 1=recalibrate drive 3 |
| 4-6 | unused |
| 7 | 1=working interrupt flag |
0040:003f - Floppy motor status
| bit | description |
|---|---|
| 0 | 1=drive 0 motor on |
| 1 | 1=drive 1 motor on |
| 2 | 1=drive 2 motor on |
| 3 | 1=drive 3 motor on |
| 4-6 | unused |
| 7 | 1=write operation |
0040:0041 - status of last diskette operation
| bit | description |
|---|---|
| 0 | invalid diskette command |
| 1 | diskette address mark not found |
| 2 | sector not found |
| 3 | diskette DMA error |
| 4 | CRC check / data error |
| 5 | diskette controller failure |
| 6 | seek to track failed |
| 7 | diskette time-out |
Video Information Table
| Address | Size | Description |
|---|---|---|
| 40:49 | byte | Current video mode (see VIDEO MODE) |
| 40:4A | word | Number of screen columns |
| 40:4C | word | Size of current video regen buffer in bytes |
| 40:4E | word | Offset of current video page in video regen buffer |
| 40:50 | 8 words | Cursor position of pages 1-8, high order byte=row low order byte=column; changing this data isn't reflected immediately on the display |
| 40:60 | byte | Cursor ending (bottom) scan line (don't modify) |
| 40:61 | byte | Cursor starting (top) scan line (don't modify) |
| 40:62 | byte | Active display page number |
| 40:63 | word | Base port address for active 6845 CRT controller 3B4h = mono, 3D4h = color |
| 40:65 | byte | 6845 CRT mode control register value (port 3x8h) EGA/VGA values emulate those of the MDA/CGA |
| 40:66 | byte | CGA current color palette mask setting (port 3d9h) EGA and VGA values emulate the CGA |
Details
0040:0087 - Video mode options (EGA+)
| bit | description |
|---|---|
| 0 | 1=alphanumeric cursor emulation enabled |
| 1 | 1=video subsystem attached to monochrome |
| 2 | reserved |
| 3 | 1=video subsystem is inactive |
| 4 | reserved |
| 5-6 | video RAM: 00-64Kb; 10-192Kb; 01-128Kb; 11-256Kb |
| 7 | video mode number passed to INT 10, function 0 |
0040:0088 - EGA feature bit switches (EGA+)
| bit | description |
|---|---|
| 0 | EGA SW1 config (1=off) |
| 1 | EGA SW2 config (1=off) |
| 2 | EGA SW3 config (1=off) |
| 3 | EGA SW4 config (1=off) |
| 4 | Input FEAT0 (ISR0 bit 5) after output on FCR0 |
| 5 | Input FEAT0 (ISR0 bit 6) after output on FCR0 |
| 6 | Input FEAT1 (ISR0 bit 5) after output on FCR1 |
| 7 | Input FEAT1 (ISR0 bit 6) after output on FCR1 |
0040:0089 - Video display data area (MCGA and VGA)
| bit | description |
|---|---|
| 0 | 1=VGA is active |
| 1 | 1=gray scale is enabled |
| 2 | 1=using monochrome monitor |
| 3 | 1=default palette loading is disabled |
| 4 | see table below |
| 5 | reserved |
| 6 | see table below |
| 7 | alphanumeric scan lines (see table below) |
| bit 7 | bit 4 | Scan Lines |
|---|---|---|
| 0 | 0 | 350 line mode |
| 0 | 1 | 400 line mode |
| 1 | 0 | 200 line mode |
| 1 | 1 | reserved |
EGA / VGA Related Tables
Video Save/Override Pointer Table (pointer at 40:A8):
| 00 | dword | Video Parameter Table pointer |
| 04 | dword | Dynamic Parameter Save Area pointer (EGA, VGA) |
| 08 | dword | Alphanumeric Character Set Override pointer |
| 0C | dword | Graphics Character Set Override pointer |
| 10 | dword | Secondary Save Pointer Table pointer (VGA) |
| 14 | dword | reserved, set to 0000:0000 |
| 18 | dword | reserved, set to 0000:0000 |
Video Parameter Table
| 00 | byte | number of displayed character columns |
| 01 | byte | number of displayed screen rows minus 1 |
| 02 | byte | character matrix height in points |
| 03 | word | video buffer size in bytes |
| 05 | dword | contents of sequencer registers 1-4 |
| 09 | byte | misc. output register values |
| 0A | 25 bytes | contents of CRTC registers 0-18h |
| 23 | 20 bytes | contents of attribute controller regs 0-13h |
| 37 | 9 bytes | contents of graphics controller regs 0-8 |
0040:0072 - Soft reset flag
| value | description |
|---|---|
| 1234h | Bypass memory tests & CRT initialization |
| 4321h | Preserve memory |
| 5678h | System suspend |
| 9ABCh | Manufacturer test |
| ABCDh | Convertible POST loop |
| ????h | many other values are used during POST |
Dynamic Parameter Save Area
| 00 | 16 bytes | contents of graphics controller pallette regs |
| 10 | byte | contents of graphics controller overscan reg |
| 11 | 239 bytes | reserved |
Alphanumeric Character Set Override
| 00 | byte | length of each character definition in bytes |
| 01 | byte | character generator RAM bank |
| 02 | word | count of characters defined |
| 04 | word | first character code in table |
| 06 | dword | pointer to character font definition table |
| 0A | byte | number of character rows displayed |
| 0B | nbytes | array of applicable video modes |
| 0B+n | byte | FFh end of mode list marker |
Graphics Character Set Override
| 00 | byte | count of displayed character rows |
| 01 | word | length of each character definition in bytes |
| 03 | dword | pointer to character font definition table |
| 07 | nbytes | array of applicable video modes |
| 07+n | byte | FFh end of mode list marker |
Secondary Save Pointer Table
| 00 | word | length of table in bytes |
| 02 | dword | pointer to display combination code table |
| 06 | dword | pointer to secondary alphanumeric char set override |
| 0A | dword | pointer to user palette profile table (VGA) |
| 0E | dword | reserved |
| 12 | dword | reserved |
| 16 | dword | reserved |
Display Combination Code Table
| 00 | byte | number of table entries |
| 01 | byte | DCC table version number |
| 02 | byte | maximum display type code |
| 03 | byte | reserved |
| 04 | n words | array valid display combinations: |
| 0,0 | entry | 0 | no display |
| 0,1 | entry | 1 | MDPA |
| 0,2 | entry | 2 | CGA |
| 2,1 | entry | 3 | MDPA + CGA |
| 0,4 | entry | 4 | EGA |
| 4,1 | entry | 5 | EGA + MDPA |
| 0,5 | entry | 6 | MEGA |
| 2,5 | entry | 7 | MEGA + CGA |
| 0,6 | entry | 8 | PGC |
| 1,6 | entry | 9 | PGC + MDPA |
| 5,6 | entry | 10 | PGC + MEGA |
| 0,8 | entry | 11 | CVGA |
| 1,8 | entry | 12 | CVGA + MDPA |
| 0,7 | entry | 13 | MVGA |
| 2,7 | entry | 14 | MVGA + CGA |
| 2,6 | entry | 15 | MVGA + PGC |
Secondary Alpha Mode Auxillary Character Generator Table
| 00 | byte | bytes per character |
| 01 | byte | block to load |
| 02 | byte | reserved |
| 03 | dword | font table pointer |
| 07 | nbytes | array of mode values for this font |
| 07+n | byte | FFh end of mode list marker |
Palette Profile Table (VGA only)
| 00 | byte | 1 - enable underlining in all alphanumeric modes 0 - enable underlining in monochrome alpha modes -1 - disable underlining in all alpha modes |
| 01 | byte | reserved |
| 02 | word | reserved |
| 04 | word | count of attribute controller regs in table |
| 06 | word | first attribute controller register number |
| 08 | dword | pointer to attribute controller reg table |
| 0C | word | count of video DAC color registers in table |
| 0E | word | first video DAC color register number |
| 10 | dword | video DAC color register table pointer |
| 14 | nbytes | array of applicable video modes for this font |
| 14+n | byte | FFh end of video mode list marker |
- see also BIOS Data Area
- see INT 10,1B for Dynamic Video State Table and Video Static Functionality Table
Others Information Table
| Address | Size | Description |
|---|---|---|
| 40:67 | dword | CS:IP for 286 return from protected mode |
| dword | Temp storage for SS:SP during shutdown | |
| dword | Day counter on all products after AT | |
| dword | PS/2 Pointer to reset code with memory preserved | |
| 5 bytes | Cassette tape control (before AT) | |
| 40:6C | dword | Daily timer counter, equal to zero at midnight; incremented by INT 8; read/set by INT 1A |
| 40:70 | byte | Clock rollover flag, set when 40:6C exceeds 24hrs |
| 40:71 | byte | BIOS break flag, bit 7 is set if Ctrl-Break was *ever* hit; set by INT 9 |
| 40:72 | word | Soft reset flag via Ctl-Alt-Del or JMP FFFF:0 (see below) |
| 40:74 | byte | Status of last hard disk operation (see INT 13,1) |
| 40:75 | byte | Number of hard disks attached |
| 40:76 | byte | XT fixed disk drive control byte |
| 40:77 | byte | Port offset to current fixed disk adapter |
| 40:78 | 4 bytes | Time-Out value for LPT1,LPT2,LPT3(,LPT4 except PS/2) |
| 40:7C | 4 bytes | Time-Out value for COM1,COM2,COM3,COM4 |
| 40:80 | word | Keyboard buffer start offset (seg=40h,BIOS 10-27-82) |
| 40:82 | word | Keyboard buffer end offset (seg=40h,BIOS 10-27-82) |
| 40:84 | byte | Rows on the screen (less 1, EGA+) |
| 40:85 | word | Point height of character matrix (EGA+) |
| byte | PCjr: character to be repeated if the typematic repeat key takes effect | |
| 40:86 | byte | PCjr: initial delay before repeat key action begins |
| 40:87 | byte | PCjr: current Fn function key number |
| Video mode options (EGA+) (see below) | ||
| 40:88 | byte | PCjr: third keyboard status byte EGA feature bit switches, emulated on VGA (see below) |
| 40:89 | byte | Video display data area (MCGA and VGA) (see below) |
| 40:8A | byte | Display Combination Code (DCC) table index (EGA+) |
| 40:8B | byte | Last diskette data rate selected |
| 40:8C | byte | Hard disk status returned by controller |
| 40:8D | byte | Hard disk error returned by controller |
| 40:8E | byte | Hard disk interrupt control flag(bit 7=working int) |
| 40:8F | byte | Combination hard/floppy disk card when bit 0 set |
| 40:90 | 4 bytes | Drive 0,1,2,3 media state |
| 40:94 | byte | Track currently seeked to on drive 0 |
| 40:95 | byte | Track currently seeked to on drive 1 |
| 40:96 | byte | Keyboard mode/type |
| 40:97 | byte | Keyboard LED flags |
| 40:98 | dword | Pointer to user wait complete flag |
| 40:9C | dword | User wait Time-Out value in microseconds |
| 40:A0 | byte | RTC wait function flag |
| 40:A1 | byte | LANA DMA channel flags |
| 40:A2 | 2 bytes | Status of LANA 0,1 |
| 40:A4 | dword | Saved hard disk interrupt vector |
| 40:A8 | dword | BIOS Video Save/Override Pointer Table address (see VIDEO TABLES) |
| 40:AC | 8 bytes | Reserved |
| 40:B4 | byte | Keyboard NMI control flags (convertible) |
| 40:B5 | dword | Keyboard break pending flags (convertible) |
| 40:B9 | byte | Port 60 single byte queue (convertible) |
| 40:BA | byte | Scan code of last key (convertible) |
| 40:BB | byte | NMI buffer head pointer (convertible) |
| 40:BC | byte | NMI buffer tail pointer (convertible) |
| 40:BD | 16bytes | NMI scan code buffer (convertible) |
| 40:CE | word | Day counter (convertible and after) |
| 40:F0 | 16bytes | Intra-Applications Communications Area (IBM Technical Reference incorrectly locates this at 50:F0-50:FF) |
| 50:00 | byte | Print screen status byte 00 = PrtSc not active, 01 = PrtSc in progress FF = error |
| 50:01 | 3 bytes | Used by BASIC |
| 50:04 | byte | DOS single diskette mode flag, 0=A:, 1=B: |
| 50:05 | 10bytes | POST work area |
| 50:0F | byte | BASIC shell flag; set to 2 if current shell |
| 50:10 | word | BASICs default DS value (DEF SEG) |
| 50:12 | dword | Pointer to BASIC INT 1C interrupt handler |
| 50:16 | dword | Pointer to BASIC INT 23 interrupt handler |
| 50:1A | dword | Pointer to BASIC INT 24 disk error handler |
| 50:20 | word | DOS dynamic storage |
| 50:22 | 14bytes | DOS diskette initialization table (INT 1E) |
| 50:30 | 4bytes | MODE command |
| 70:00 | I/O drivers from IO.SYS/IBMBIO.COM |
Floppy disk controller
| 40:8B | byte | Last diskette data rate selected |
|7|6|5|4|3|2|1|0| last diskette data rate selected | | | | `--------- reserved | | `------------ last floppy drive step rate selected `-------------- last floppy data rate selected
| Data | Rate | Step Rate | |
|---|---|---|---|
| 00 | 500K bps | 00 | step rate time of 0C |
| 01 | 300K bps | 01 | step rate time of 0D |
| 10 | 250K bps | 10 | step rate time of 0A |
| 11 | reserved | 11 | reserved |
| Address | Size | Description |
|---|---|---|
| 40:8C | byte | Hard disk status returned by controller |
| 40:8D | byte | Hard disk error returned by controller |
| 40:8E | byte | Hard disk interrupt control flag(bit 7=working int) |
| 40:8F | byte | Combination hard/floppy disk card when bit 0 set |
| 40:90 | 4 bytes | Drive 0,1,2,3 media state |
|7|6|5|4|3|2|1|0| drive media state (4 copies) | | | | | `------- drive/media state (see below) | | | | `------- reserved | | | `------- 1=media/drive established | | `------- double stepping required `--------- data rate: 00=500K bps 01=300K bps 10=250K bps 11=reserved
| Bits 210 | Drive Media State |
|---|---|
| 000 | 360Kb diskette/360Kb drive not established |
| 001 | 360Kb diskette/1.2Mb drive not established |
| 010 | 1.2Mb diskette/1.2Mb drive not established |
| 011 | 360Kb diskette/360Kb drive established |
| 100 | 360Kb diskette/1.2Mb drive established |
| 101 | 1.2Mb diskette/1.2Mb drive established |
| 110 | Reserved |
| 111 | None of the above |
| Address | Size | Description |
|---|---|---|
| 40:94 | byte | Track currently seeked to on drive 0 |
| 40:95 | byte | Track currently seeked to on drive 1 |
| 40:96 | byte | Keyboard mode/type |
|7|6|5|4|3|2|1|0| Keyboard mode/type | | | | | | | `--- last code was the E1 hidden code | | | | | | `---- last code was the E0 hidden code | | | | | `----- right CTRL key depressed | | | | `------ right ALT key depressed | | | `------- 101/102 enhanced keyboard installed | | `-------- force num-lock if Rd ID & KBX | `--------- last char was first ID char `---------- read ID in process
| Address | Size | Description |
|---|---|---|
| 40:97 | byte | Keyboard LED flags |
|7|6|5|4|3|2|1|0| Keyboard LED flags | | | | | | | `--- scroll lock indicator | | | | | | `---- num-lock indicator | | | | | `----- caps-lock indicator | | | | `------ circus system indicator | | | `------- ACK received | | `-------- re-send received flag | `--------- mode indicator update `---------- keyboard transmit error flag
| Address | Size | Description |
|---|---|---|
| 40:98 | dword | Pointer to user wait complete flag |
| 40:9C | dword | User wait Time-Out value in microseconds |
| 40:A0 | byte | RTC wait function flag |
|7|6|5|4|3|2|1|0| INT 15,86 RTC wait function flag | | | | | | | `--- 1= wait pending | `-------------- not used `--------------- 1=INT 15,86 wait time elapsed
| Address | Size | Description |
|---|---|---|
| 40:A1 | byte | LANA DMA channel flags |
| 40:A2 | 2 bytes | Status of LANA 0,1 |
| 40:A4 | dword | Saved hard disk interrupt vector |
| 40:A8 | dword | BIOS Video Save/Override Pointer Table address (see VIDEO TABLES) |
| 40:AC | 8 bytes | Reserved |
| 40:B4 | byte | Keyboard NMI control flags (convertible) |
| 40:B5 | dword | Keyboard break pending flags (convertible) |
| 40:B9 | byte | Port 60 single byte queue (convertible) |
| 40:BA | byte | Scan code of last key (convertible) |
| 40:BB | byte | NMI buffer head pointer (convertible) |
| 40:BC | byte | NMI buffer tail pointer (convertible) |
| 40:BD | 16 bytes | NMI scan code buffer (convertible) |
| 40:CE | word | Day counter (convertible and after) |
| 40:F0 | 16 bytes | Intra-Applications Communications Area (IBM Technical Reference incorrectly locates this at 50:F0-50:FF) |
| Address | Size | Description |
|---|---|---|
| 50:00 | byte | Print screen status byte 00 = PrtSc not active, 01 = PrtSc in progress FF = error |
| 50:01 | 3 bytes | Used by BASIC |
| 50:04 | byte | DOS single diskette mode flag, 0=A:, 1=B: |
| 50:05 | 10 bytes | POST work area |
| 50:0F | byte | BASIC shell flag; set to 2 if current shell |
| 50:10 | word | BASICs default DS value (DEF SEG) |
| 50:12 | dword | Pointer to BASIC INT 1C interrupt handler |
| 50:16 | dword | Pointer to BASIC INT 23 interrupt handler |
| 50:1A | dword | Pointer to BASIC INT 24 disk error handler |
| 50:20 | word | DOS dynamic storage |
| 50:22 | 14 bytes | DOS diskette initialization table (INT 1E) |
| 50:30 | 4 bytes | MODE command |
| 70:00 | I/O drivers from IO.SYS/IBMBIO.COM |
The following map varies in size and locus
| Address | Size | Description |
|---|---|---|
| 07C0:0 | Boot code is loaded here at startup (31k mark) | |
| A000:0 | EGA/VGA RAM for graphics display mode 0Dh & above | |
| B000:0 | MDA RAM, Hercules graphics display RAM | |
| B800:0 | CGA display RAM | |
| C000:0 | EGA/VGA BIOS ROM (thru C7FF) | |
| C400:0 | Video adapter ROM space | |
| C600:0 | 256 bytes | PGA communication area |
| C800:0 | 16 Kb | Hard disk adapter BIOS ROM |
| C800:5 | XT Hard disk ROM format, AH=Drive, AL=Interleave | |
| D000:0 | 32 Kb | Cluster adapter BIOS ROM |
| D800:0 | PCjr conventionalsoftware cartridge address | |
| E000:0 | 64 Kb | Expansion ROM space (hardwired on AT+) |
| 128 Kb | PS/2 System ROM (thru F000) | |
| F000:0 | System monitor ROM PCjr: software cartridge override address |
|
| F400:0 | System expansion ROMs | |
| F600:0 | IBM ROM BASIC (AT) | |
| F800:0 | PCjr software cartridge override address | |
| FC00:0 | BIOS ROM | |
| FF00:0 | System ROM | |
| FFA6:E | ROM graphics character table | |
| FFFF:0 | ROM bootstrap code | |
| FFFF:5 | 8 bytes | ROM date (not applicable for all clones) |
| FFFF:E | byte | ROM machine id (see MACHINE ID) |
back2root/ibm-pc-ms-dos/hardware/informations/bios_data_area.1673957673.txt.gz · Dernière modification : 2023/01/17 13:14 de frater
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