The Intel/Microsoft Advanced Power Management functions indicate failure
by setting the Carry Flag and returning one of following error codes in
the AH register:

01H APM functionality disabled

02H Interface connection already established
03H Interface not connected
04H Real mode connection not established
05H 16-bit protected-mode interface already established
06H 16-bit protected-mode interface not supported
07H 32-bit protected-mode interface already established
08H 32-bit protected-mode interface not supported

09H Unrecognized APM Device ID
0aH Parameter in CX is out of range

60H Can't enter requested state

80H No power management events pending

86H (reserved) no APM present

See Also: APM API
INT 15H (Misc AT Services)
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APM API Error/Return Codes