A and ACC both represent accumulators with the same address, but in the assembly, the writing of A and ACC has different meanings.

The instruction contains a, and the instruction code is different; On the other hand, ACC appears as an operand and represents an address.

Equivalent to assembly instructions, including MOV A and RN, as well as MOV Direct and RN.

MOV A, R0 and MOV ACC, R0 will generate the above two different machine codes, but the result is the same.

That's a better understanding of ADA. Adding A and ACC uses the instruction ADD A and direct, which is the address indicated by ACC symbol, that is, the accumulator adds itself, which is equivalent to X2, that is, it moves left.