Casio IT-2000D - Manual (Page 224)

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DX = Remaining battery life - time unit
bit 15 = 0 : Time unit is in second.
1 : Time unit is in minute
bits 14 to 0 = value for second or minutes
0 to 7FFFh : Valid value for second or minute
FFh : Unknown
If function unsuccessful:
Carry = 1
AH = Error code
09h : Unrecognized device ID