Download Crate CSM16 Specifications

5
Legacy BIOS References
5.1
BIOS INTs
This document lists only the INTs to be supported and does not list all subfunctions
unless they are not required. Refer to the IBM* Personal System/2 and Personal
Computer BIOS Interface Technical Reference or any of the AMI* or Phoenix* BIOS
manuals for full information on all subfunctions.
INT 0x02 - NMI
There needs to be a NMI handler.
INT 0x05 - Print Screen
This INT must be supported. Note that this INT modifies memory location 50:00.
Memory Location 50:00
This is a Byte memory location. A value of 0x00 indicates that the print screen
successfully completed or was not invoked. A value of 0x01 indicates that a print screen
is in progress and subsequent print screens are ignored. A value of 0xFF indicates that
the print screen terminated due to an error.
INT 0x08 - System Timer
This INT must be supported. Note that this INT modifies memory locations 40:6C,
40:70, 40:40, and 40:3F. It also invokes software INT 1C.
Memory Location 40:6C
This location is a Dword memory location. The value is incremented every INT 08 tick or
18.2 times a second. The memory location is reset to 0x00000000 when a 24-hour
duration has elapsed.
Memory Location 40:70
This location is a Byte memory location. This location has a value of 0x00 until a 24hour duration has elapsed. It is then set to 0x01. The byte must be manually reset
back to 0x00.
Memory Location 40:40
This location is a Byte memory location. The value is decremented every INT 08 tick or
18.2 times a second. If the timer goes to 0x00, the floppy motor is turned off and resets
the floppy flags in memory location 40:3F.
Memory Location 40:3F
This location is a Byte memory location. Bit 1 is set if drive B motor is on. Bit 0 is set if
drive A motor is on.
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