Block Copy // LDD (LoaD and Decrement)
This 2-byte instruction transfers a byte of data from the memory location addressed by the contents of the HL register pair to the memory location addressed by the contents of the DE register pair. Then both of these register pairs including the Byte Counter (BC) Register pair are decremented.
If the HL register pair contains 1111h, memory location 1111h contains byte 88h, the DE register pair contains 2222h, memory location 2222h contains byte 66h, and the BC register pair contains 7h, then instruction LDD results in the following contents in register pairs and memory addresses: HL contains 1110h (1111h) contains 88h DE contains 2221h (2222h) contains 88h BC contains 6h