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15DA20

Category: vendor-specific BIOS extensions
Flags: Undocumented function

INT 15 - AMI PCI BIOS v1.00.12.AX1T - CMOS RAM BITFIELD MANIPULATION

	AX = DA20h
	BL = subfunction
	    00h set CMOS data field
		BH = CMOS data field number (00h-4Dh)
		CH = new value for bitfield (in lowest bits of register)
	    01h read CMOS data field
		BH = CMOS data field number (00h-4Dh)
		Return: CH = value of bitfield
			CL = mask of valid bits
		Note:	both CL/CH shifted to move valid bits into lowest pos
	    02h set CMOS byte
		CL = CMOS RAM address (00h-7Fh)
		CH = new value for CMOS byte
	    03h get CMOS byte
		CL = CMOS RAM address (00h-7Fh)
		Return: CH = value of CMOS byte
	    04h update CMOS checksums
		Note:	sets 2Eh/2Fh to checksum of 10h-2Dh and 7Eh/7Fh to
			  checksum of 48h-7Dh
	    05h verify CMOS checksums
		Return:	CF clear if checksums OK
			    AH = 00h
			CF set if checksum mismatch
			    AH = 01h
Return: CF clear if successful
	    AH = 00h
	CF set on error
	    AH = error code (86h unsupported function/data field)
Notes:	this function was not supported by the v1.00.05.AX1 BIOS, but had been
	  added by 1.00.12.AX1T
	after using subfunctions 00h or 02h, the application must call
	  subfunction 04h to update the checksums to prevent an error the next
	  time the system is booted


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  Copyright 2000   by Ralf Brown     Updated Jul 2000