These instructions perform arithmetic operations such as addition, subtraction, increment, and decrement.
Any 8-bit number, or the contents of a register or the contents of a memory location can be added to the contents of the accumulator and the sum is stored in the accumulator. No two other 8-bit registers can be added directly (e.g., the contents of register B cannot be added directly to the contents of the register C). The instruction DAD is an exception; it adds 16-bit data directly in register pairs.
ADD Add to Accumulator ADI Add Immediate Data to Accumulator ADC Add to Accumulator Using Carry Flag ACI Add Immediate data to Accumulator Using Carry
Any 8-bit number, or the contents of a register, or the contents of a memory location can be subtracted from the contents of the accumulator and the results stored in the accumulator. The subtraction is performed in 2's compliment, and the results if negative, are expressed in 2's complement. No two other registers can be subtracted directly.
SUB Subtract from Accumulator SUI Subtract Immediate Data from Accumulator SBB Subtract from Accumulator Using Borrow (Carry) Flag SBI Subtract Immediate from Accumulator Using Borrow (Carry) Flag
The 8-bit contents of a register or a memory location can be incremented or decrement by 1. Similarly, the 16-bit contents of a register pair (such as BC) can be incremented or decrement by 1. These increment and decrement operations differ from addition and subtraction in an important way; i.e., they can be performed in any one of the registers or in a memory location.
INR Increment Specified Byte by One DCR Decrement Specified Byte by One INX Increment Register Pair by One DCX Decrement Register Pair by One DAD Double Register Add; Add Content of Register Pair to H & L Register Pair
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