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back2root:ibm-pc-ms-dos:hardware:informations:bios_data_area
Table des matières
BDA - BIOS Data Area - PC Memory Map - WIP
The following map varies in size and locus
| 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 | 16K | Hard disk adapter BIOS ROM |
| C800:5 | XT Hard disk ROM format, AH=Drive, AL=Interleave | |
| D000:0 | 32K | Cluster adapter BIOS ROM |
| D800:0 | PCjr conventionalsoftware cartridge address | |
| E000:0 | 64K | Expansion ROM space (hardwired on AT+) |
| 128K | 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) |
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) |
| Equipement | ||
| 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 |
| Keyboard | ||
| 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 |
| 40:1E | 32 bytes | Keyboard buffer (circular queue buffer) |
| Drive & Diskette | ||
| 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) |
| Videos | ||
| 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 |
| PS/2 - 286+ | ||
| 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 | |
| RTC | ||
| 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 |
| EGA+ | ||
| 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+) |
| Drives | ||
| 40:8B | byte | Last diskette data rate selected (see below) |
| 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 (see below) |
| 40:94 | byte | Track currently seeked to on drive 0 |
| 40:95 | byte | Track currently seeked to on drive 1 |
| Keyboard | ||
| 40:96 | byte | Keyboard mode/type (see below) |
| 40:97 | byte | Keyboard LED flags (see below) |
| 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 (see below) |
| 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) |
| Misc | ||
| 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 | |
40:10 - 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 |
40:11 - INT 11 registers
| 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 |
40:17 - Keyboard flag 0
| bit | description | bit | description | |
|---|---|---|---|---|
| 0 | right shift key depressed | 0 | left CTRL key depressed | |
| 1 | left shift key depressed | 1 | left ALT key depressed | |
| 2 | CTRL key depressed | 2 | system key depressed and held | |
| 3 | ALT key depressed | 3 | suspend key has been toggled | |
| 4 | scroll-lock is active | 4 | scroll lock key is depressed | |
| 5 | num-lock is active | 5 | num-lock key is depressed | |
| 6 | caps-lock is active | 6 | caps-lock key is depressed | |
| 7 | insert is active | 7 | insert key is depressed |
40:18 - 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
40:3e - 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 |
40:3f - 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 |
40:41 - 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 |
Soft reset flag
40:72 - 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 |
Floppy disk controller
40:8B - Last diskette data rate selected
| bit | description |
|---|---|
| 0-3 | reserved |
| 4-5 | last floppy drive step rate selected |
| 6-7 | 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 |
40:90 - Drive 0,1,2,3 media state
| bit | description |
|---|---|
| 0-2 | drive/media state (see below) |
| 3 | reserved |
| 4 | 1=media/drive established |
| 5 | double stepping required |
| 6-7 | 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 |
Keyboard
40:96 - Keyboard mode/type
| bit | description |
|---|---|
| 0 | last code was the E1 hidden code |
| 1 | last code was the E0 hidden code |
| 2 | right CTRL key depressed |
| 3 | right ALT key depressed |
| 4 | 101/102 enhanced keyboard installed |
| 5 | force num-lock if Rd ID & KBX |
| 6 | last char was first ID char |
| 7 | read ID in process |
40:97 - Keyboard LED flags
| bit | description |
|---|---|
| 0 | scroll lock indicator |
| 1 | um-lock indicator |
| 2 | caps-lock indicator |
| 3 | circus system indicator |
| 4 | ACK received |
| 5 | re-send received flag |
| 6 | mode indicator update |
| 7 | keyboard transmit error flag |
Real Time Clock
40:A0 - RTC wait function flag
back2root/ibm-pc-ms-dos/hardware/informations/bios_data_area.txt · Dernière modification : 2024/08/13 11:23 de frater
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