Oh man, stress my aging brain cells. I haven't looked at this stuff in 40 years!
DAD, Double Register Add, adds the contents of B&C, D&E, H&L or SP to the contents of H&L and places the result in H&L. Forms are:
|DAD||B||ADD||HL,BC||09||HL <- HL + BC|
|DAD||D||ADD||HL,DE||19||HL <- HL + DE|
|DAD||H||ADD||HL,HL||29||HL <- HL + HL|
|DAD||SP||ADD||HL,SP||39||HL <- HL + SP|
It can affect the Carry bit (CY), but I don't see it touching the Accumulator at all.