Addressing modes of 8085

Define Registers of Microprocessor 8085: “ A register is a temporary or short term storage space built into a CPU.” More or less of the registers are applied internally but they cannot be accessed outside the processor. Microprocessor 8085, Image Crdit – Myself What are the Types of the Register in Microprocessor 8085? • Accumulator (8 bit) • GPR (8 bit) • SP (16 bit) • PC (16 bit) • IR (8 bit) • TR (8 bit) Microprocessor 8085 Architecture , Image Credit – Define Accumulator: In the microprocessor 8085, accumulator specified as an 8 bit register connected with an ALU. This is utilized to hold one of the operand for arithmetical and logic-operation; it works as input to the ALU. The other operand for arithmetic and logical operation possibly stored either in memory or in GPR. But the final product will be stored in the accumulator only. Register in Define General Purpose Register (GPR): 8085 microprocessor has 8 bit GPR; it works like a pair – B-C, D-E, H-L The H-L register pair is used as a memory pointer & it holds 16 bit address of a memory location. Define Stack Pointer (SP): Stack pointer is a 16 bit especial purpose register. Stack is a order of memory location set by a programmer. The stack also perform as LIFO (Last in First Out ). Here two operations are used; PUSH & POP. Program Counter Definition: A 16 bit register for specified operations ; comprises registers to load memory address from wherever the subsequent instruction is to be fetched. Assume the program co...

The addressing modes of 8085 microprocessor can be classified into five. They are immediate addressing, register addressing, direct addressing, indirect addressing, and implied addressing. All 8085 addressing modes are described below. Before that what is an addressing mode in a microprocessor. What is an Addressing Mode in a Microprocessor? The addressing mode of a microprocessor defines the way in which the operand of instructions can be accessed. 8085 Microprocessor Addressing Modes The five types of addressing modes of 8085 microprocessor is given below. 1.Immediate Addressing Mode In the immediate addressing mode, the data is stored along with the instruction. And the data is directly transferred to the register. • Here the data can be either 8 bit or 16 bit. • In the case of 16-bit data, the lower byte is stored the first position and the higher byte is stored in the next position. Example: MVI A 0FH; Load OFH to reg Accumulator. another example, LXI D FFF0H; load FFF0H to the D-E reg pair. Here F0H– Lower byte and FFH– Higher byte. After the execution of the above instructions, (A) = 0FH and (D)(E)=FFF0H. 2. Register Addressing Mode In the register addressing mode, the data is copied from one register and stored in another register (or register pair). Example: MOV B, D; move the contents of register D to register B. another example, INX H; Increment the contents of H-L register pair. Originally, (B) = 0FH and (D) = 1FH and (H) = 0FH and (L) = 1AH After the execution...

Addressing Modes of 8085 Microprocessor: Part of the programming flexibility for each microprocessor is the number and different kind of ways the programmer can refer to data stored in the memory. The different ways that a microprocessor can access data are referred to as addressing modes. Addressing Modes of 8085 Microprocessor are : • Immediate Addressing Mode in 8085 • Register Addressing Mode in 8085 • Direct Addressing Mode in 8085 • Indirect Addressing Mode in 8085 • Implied Addressing Mode in 8085 1. Immediate Addressing Mode in 8085: In an Immediate Addressing Modes of 8085 Microprocessor, 8 or 16 bit data can be specified as a part of instruction. In 8085, the instructions having ‘I’ letter fall under this category. ‘I’ indicates immediate addressing mode. 2. Register Addressing Mode in 8085: Another Types of Addressing Modes in 8085 is Register Addressing Mode in 8085 which specifies the source operand, destination operand, or both to be contained in an 8085 registers. This results in faster execution, since it is not necessary to access memory locations for operands. 3. Direct Addressing Mode in 8085: The Direct Addressing Mode in 8085 specifies the 16 bit address of the operand within the instruction itself. The second and third bytes of instruction contain this 16 bit address. 4. Indirect Addressing Mode in 8085: In Indirect Addressing Mode in 8085, the memory address where the operand located is specified by the contents of a register pair.

• • • • • • Direct memory Addressing • Register direct addressing • Register indirect addressing • Immediate addressing Direct Addressing Mode In Direct memory Addressing mode, the address of the operand (data) is given in the instruction itself. Example: STA 8086H (stores the content of the accumulator in the memory location 2400H). Machine Code = 32,86,80. The first byte is for the Opcode while the 2nd and 3rd byte is used to specify the address of the memory location. The source of the data is the accumulator, from which the data will be stored in the memory location 8086 H. Register Addressing Mode In Register Direct Addressing mode the operand is either one of the general purpose register or the accumulator. The address of the register on which the operation is to be performed is specified in the Opcode itself. Therefore, it is 1-byte instruction. Examples: MOV A, B (move the content of the register B to register A). Machine code = 78. The Data source is B and the data will be moved to register A. The data is moved directly from one register to another. Register Indirect Addressing Mode In Register Indirect Addressing mode the data cannot be retrieved directly from the register, unlike the Register direct AM. The address of the data is stored in a register pair. The Control Unit of the CPU will first fetch the register pair and then fetch the data from the address specified by register pair. Example: LXI H, 8051H (load H-L pair with 8051 ), MOV A, M (move the content ...

Addressing Modes– The term addressing modes refers to the way in which the operand of an instruction is specified. The addressing mode specifies a rule for interpreting or modifying the address field of the instruction before the operand is actually executed. Addressing modes for 8086 instructions are divided into two categories: The 8086 memory addressing modes provide flexible access to memory, allowing you to easily access variables, arrays, records, pointers, and other complex data types. The key to good assembly language programming is the proper use of memory addressing modes. An assembly language program instruction consists of two parts The memory address of an operand consists of two components: IMPORTANT TERMS • Starting address of memory segment. • Effective address or Offset: An offset is determined by adding any combination of three address elements: displacement, base and index. • Displacement: It is an 8 bit or 16 bit immediate value given in the instruction. • Base: Contents of base register, BX or BP. • Index: Content of index register SI or DI. According to different ways of specifying an operand by 8086 microprocessor, different addressing modes are used by 8086. Addressing modes used by 8086 microprocessor are discussed below: • Implied mode:: In implied addressing the operand is specified in the instruction itself. In this mode the data is 8 bits or 16 bits long and data is the part of instruction.Zero address instruction are designed with implied addr...

1. Operation to be performed. 2. Address of source of data. 3. Address of destination of the result. The method by which the address of the source of data or the address of the destination of the result is given in the instruction is called addressing modes. The term addressing mode refers to the way in which the operand of the instruction is specified. Types of Addressing Modes The 8085 microprocessor has the following five types of addressing: 1. Register direct addressing 2. Direct addressing 3. Immediate addressing 4. Indirect addressing 5. Implicit addressing Register Direct Addressing If the address of data is given in the form of a register in the instruction than it is called as register direct addressing mode. Example: MOV B, C It copies the content of register C to register B. Direct Addressing mode If the address of data is directly given in the instruction than it is called as direct addressing mode. Example: IN 25 H Here 25 H is the 8-bit address. Immediate Addressing mode In this addressing mode, the data itself given in the instruction. Example: MVI A, 9A H Note: If opcode has the last character ‘ I” then it is immediate addressing mode but vice-versa is not true. Indirect Addressing mode If the address of data given in the form of content of a register in the instruction than this type is called Indirect Addressing mode. It is also called as Register indirect or indirect register addressing mode. Example: MOV B, M Here the data is in the memory location poi...