Arithmetic Group of Instructions

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Arithmetic group of instruction has total of 14 instruction types which are further extended to 64 instructions. They are:

Instructions to perform addition.

Instructions to performs subtraction.

Instruction to perform decimal addition.

8085 is primitive microprocessor. In its arithmetic group of instructions it has only add and subtract type of instructions. it does not have instructions to multiply or divide numbers. In this section we discuss addition type of instructions.

8085 imposes the restriction that one of the operands must be in the accumulator. The other operand can be one of the following

Contents of an 8-bit register.
Contents of memory location pointed by HL register pair.
Eight bit immediate data.

ADD is a mnemonic that stands for Add contents of R to accumulator. In this case R stands for any of the following register pairs or memory location M pointed by HL pair.

R= A,B,C,D,E,H,L or M

This instruction is used to add contents of R and accumulator. Finally the result of addition is stored in accumulator. As R can have any of eight values, there are eight opcodes for this type of instruction. It occupies only 1-byte in memory. ADD E is an example instruction of this type.

The result of execution is shown below.

Summary:

ADD R( 1-byte; ADD E; 8 opcode)

ADI is a mnemonic, which stands for ADd Immediate to Accumulator and d8 stands for any 8-bit data. This instruction is used to add 8-bit immediate data to the accumulator. The result of addition will be stored in accumulator. The flags are affected based on the results.

Example of this instruction is ADI F3H.

Summary:

ADI d8( 2-bytes; ADI F3H; 1 opcode)

INR is a mnemonic that stands for INcRement and R stands for any of the following registers or memory location M pointed by HL pair.

R=A,B,C,D,E,H,L or M

This instruction is used to add 1 to the contents of R. The result of increment will be stored in R.

All flags, except CY, flag are affected depending on the results.

Example of this instruction is INR M.

Summary:

INR R( 1-byte; INR M; 8 opcodes)

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