Addition and subtraction overflow is for signed numbers. For example, when 8-bit signed data is added or subtracted, the result cannot be expressed by 8-bit signed number, and overflow occurs. The range of 8-bit signed numbers is:-128~ 127. When calculating 127+ 1, the result is 128, and the signed data 128 cannot be represented by an 8-bit register, resulting in overflow. Calculate-120- 10, and the result is-130. The signed data-130 cannot be represented by an 8-bit register, resulting in overflow. Similarly, the signed number of 16 bits ranges from -32768 to 32767.