PC Compatible ROM BIOS Data Area Map (1988)

Report Error and General Enquiry

Michael L. Mohle' Princeton-Galax Systems
9 Grover Ave Princeton, NJ 08540
Source: BEA751

ROM BIOS Data Area Map (0400-04EF)

AddressLnFunction
040008COM1, COM2, COM3, COM4 Base I/O-addresses
040808LPT1, LPT2, LPT3, LPT4 Base I/O-addresses
041002
EQUIPMENT Flags76543210 76543210
#printersC0 xx...... ........
Serial printer20 ..x..... ........
Game adapter10 ...x.... ........
# Serial ports0E ....xxx. ........
No DMA01 .......x ........
# Diskette drivesC0 ........ xx...... (00=1, 01=2, 10=3, 11=4)
Initial video mode30 ........ ..xx.... (10=Co80, 11=Mono)
Not used0C ........ ....xx..
Math coprocessor02 ........ ......x.
Disk drives present01 ........ .......x
041201BOOT flags
041302RAM Installed (kb)
041502BOOT error flags
041702
KEYBOARD Status76543210 76543210
Insert80 x....... ........
Caps Lock40 .x...... ........
Num Lock20 ..x..... ........
Scroll Lock10 ...x.... ........
Alt shift08 ....x... ........
Ctrl shift04 .....x.. ........
Shift (left)02 ......x. ........
Shift (right)01 .......x ........
Insert80 ........ x.......
Caps Lock40 ........ .x......
Num Lock20 ........ ..x.....
Scroll Lock10 ........ ...x....
Ctrl Num Lock08 ........ ....x... (hold state)
Not used04 ........ .....xxx
041901KEYBOARD Alternate (reserved)
041A02KEYBOARD Buffer Head
041C02KEYBOARD Buffer Tail
041E20KEYBOARD 16-key Circular Buffer
043E01DISKETTE Recalibrate bits 0-3
043F01DISKETTE Motor bits 0-3
044001DISKETTE Motor count
044101DISKETTE Error status
044207DISKETTE Controller status
044901
VIDEO CGA/MDA display modePagesCharsPixels
00 = CGA 2-color (EGA 16-color) A/N text840x25320x200
01 = CGA 16-color A/N text840x25320x200
02 = CGA 2-color (EGA 16-color) A/N text4/880x25640x200
03 = CGA 16-color A/N text4/880x25640x200
04 = CGA 4-color graphics140x25320x200
05 = CGA 2-color (EGA 4-color) graphics140x25320x200
06 = CGA 2-color graphics180x25640x200
07 = MDA 2-color (EGA 4-color) graphics480x25720x350
08 = CGA 16-color graphics (undocumented)? 160x200
09 = CGA 16-color graphics (undocumented)? 320x200
0A = PC-JR   
0B   
0C   
0D   
0E   
0F   
00 = 16/64-color 8x14 text EGA B800840x25320x350
01 = 16/64-color 8x14 text EGA B800840x25320x350
02 = 16/64-color 8x14 text EGA B8004/880x25640x350
03 = 16/64-color 8x14 text EGA B8004/880x25640x350
04 = 4-color graphics CGA B800140x25320x200
05 = 4-color graphics CGA B800140x25320x200
06 = 2-color graphics CGA B800180x25640x200
07 = 4-shade mono 9x14 text MDA B0004/880x25720x350
08   
09   
0A = 4/16 or 16/64-color graphics EGA A0001/280x25640x350
0B   
0C   
0D = 16-color graphics CGA A0002/4/840x25320x200
0E = 16-color graphics CGA A0001/2/480x25640x200
0F = 4-shade mono graphics MDA A0001/280x25640x200
10 = 16/64-color graphics EGA A0002/4/880x25640x200
044A02VIDEO Screen-width in columns
044C02VIDEO Screen regeneration-length
044E02VIDEO Screen location offset (current page)
045010VIDEO Screen page 0-7 cursor locations as col:row bytes
046002VIDEO Screen cursor start:end row bytes
046201VIDEO Current screen page
046302VIDEO Video-controller port-address
046501VIDEO Current CRT mode
046601VIDEO Color-palette mask
046705BOOT Work area
046C04CLOCK Master-count DWORD
047001CLOCK Roll-over flag
047101CTRL-BREAK flag (bit 7)
047202KEYBOARD Reset (1234) on Ctrl-Alt-Del
047401286 Fixed disk status
047501286 Fixed disk drive number
047601286 Fixed disk control byte
047701286 Fixed disk port offset
047805286 Parallel-port timeout
047C05286 Serial-port timeout
048004286 Additional keyboard buffer
048401VIDEO EGA Screen rows
048502VIDEO EGA Bytes per character
048702
VIDEO EGA Information76543210 76543210
Clear/not-clear regen80 x....... ........
Onboard RAM60 .xx..... ........ 00=064k, 01=128
Enhanced Keyboard10 ...x.... ........ 10=192k, 11=256k
Not active monitor08 ....x... ........
Wait for enable04 .....x.. ........
Monochrome attached02 ......x. ........
Not emulate active01 .......x ........
Feature bitsF0 ........ xxxx....
Switch settings0F ........ ....xxxx
048903Reserved
048B01286 Last diskette data rate selected
048C01286 Fixed-disk status-register
048D01286 Fixed-disk error-register
048E01286 Fixed-disk interrupt-flag
048F01286 Fixed-disk/diskette combination controller flag
049001286 Diskette drive 0 media state
049101286 Diskette drive 1 media state
049201286 Diskette drive 0 operation start state
049301286 Diskette drive 1 operation start state
049401286 Diskette drive 0 present cylinder
049501286 Diskette drive 1 present cylinder
049601286 Reserved
049701286 Additional keyboard LED flag
049804286 Real-time-clock user wait flag offset:segment
049C04286 Real-time-clock user wait flag
04A002286 Real-time-clock wait-active flag
04A206Reserved
04A804EGA DWORD pointer-save
04AC44Reserved