Specifications

66 AMD Geode™ GeodeROM Functional Specification
Non-Removable Media
32087C
6.4.2 Extended BIOS Data Area (EBDA)
Eventually, the 256-byte BDA proved to be too small and a second area, appropriately named the “Extended BIOS Data
Area” or EBDA was created. The EBDA was originally intended for storing PS/2 pointing device data. Many current systems
use this area for storing fixed disk information.
The EBDA is typically 1 KB in length. The EBDA may be larger, however it is always in multiples of 1 KB increments. The
segment where the EBDA is located is a WORD value stored at 40:0Eh. Typically this value is 9FC0h, or 1 KB below the
end of lower 640 KB RAM. The BYTE located at EBDA:0h describes the length of this area in 1 KB increments.
Note: A value of zero in the WORD sized EBDA start segment at 40:0Eh does not mean the EBDA starts at physical loca-
tion zero. It means the system does not use an EBDA.
There is no fixed format for EBDA usage other than for those locations reserved for the PS/2 pointing device.
97h BYTE Extended keyboard status byte (2 of 2):
Bit 7 = 1 if a keyboard transmit error occurred
Bit 6 = 1 if an LED update is in progress
Bit 5 = 1 if the keyboard issued a RESEND
Bit 4 = 1 if the keyboard issued an ACK
Bit 3 = Reserved
Bit 2 = Current status of CapsLock LED
Bit 1 = Current status of NumLock LED
Bit 0 = Current status of ScrollLock LED
98h DWORD Far pointer to user-specified elapsed time semaphore byte (see INT 15h Function 83h, Wait
For Event):
Bit 7 = 1 if delay is elapsed
9Ch DWORD User-specified wait Timer2: [AT, PS exc Mod 30] user wait count in 972 ns increments
A0h-FFh 5Fh
BYTEs
Reserved for OEM-specific BIOS features.
100h BYTE Print Screen Status byte.
1. Reserved for use by the fixed disk subsystem.
Table 6-3. Format of the BIOS Data Area (Continued)
Offset Size Description