Microprocessor 8085 Basics
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The document discusses the Microprocessor 8085. It describes the architecture of the 8085, which is divided into registers, an arithmetic logic unit, an instruction decoder, address buffers, interrupt control, and timing/control circuitry. It details the registers of the 8085 including general purpose, temporary, special purpose, and 16-bit registers like the program counter and stack pointer. The document also examines the ALU, instruction decoder, addressing mechanisms, interrupt handling, serial I/O, and timing control circuitry of the 8085 microprocessor.
Microprocessor 8085 Basics
- 1. Microprocessor 8085 Dr. Nilesh Bhaskarrao Bahadure https://www.sites.google.com/site/nileshbbahadure/home July 25, 2021 1 / 20
- 2. Overview 1 Basics of Microprocessor 8085 Architecture of 8085 Registers of 8085 Arithmetic Logic Unit of 8085 Instruction Decoder Address buffer Address/data buffer Increment / decrement address latch Interrupt control Serial input / output control Timing and control circuitry Pin configuration of 8085 Control & Status signal 2 / 20
- 3. Architecture of 8085 Main Slide 3 / 20
- 4. Architecture of 8085 Architecture of 8085 divided in the following groups Registers Arithmetic and logic unit Instruction decoder Address buffer Address / data buffer Increment / decrement address latch Interrupt control Serial input / output control Timing and control circuitry Main Slide 4 / 20
- 5. Registers of 8085 Main Slide 5 / 20
- 6. Registers of 8085 Registers of 8085 can be classified as General purpose registers Temporary registers 1 Temporary data registers 2 W and Z register Special purpose registers 1 Accumulator 2 Flag register 3 Instruction registers 16 Bit registers 1 Program counter 2 Stack pointer Main Slide 6 / 20
- 7. Special Purpose Registers of 8085 I 1 Accumulator it is a 8 bit register. It is extensively used in arithmetic, logical, load and store operations as well as input / output (I/O) operations. Most of the times the result of arithmetic and logical operations is stored in register A. hence it is also identified as accumulator. 2 Flag Register It is an 8 - bit register, in which five of the bits carry significant information in the form of flags: S (sign flag), Z (zero flag), AC (Auxiliary carry flag), P (Parity flag) and CY (carry flag). 3 Instruction Register in a typical processor operation, the processor first fetches the opcode of instruction from memory. The CPU stores this opcode in a register called an instruction register. The opcode is further sent to the instruction decoder to select one of the 256 alternatives. 7 / 20
- 8. Special Purpose Registers of 8085 II Main Slide 8 / 20
- 9. 16 - bit registers 1 Program Counter (PC): Program is sequence of instructions. As mentioned earlier, microprocessor fetches these instructions from the memory and executes them sequentially. The program counter is a special purpose register which, at a given time, stores the address of the next instruction to be fetched. Program counter acts as a pointer to the next instruction. How processor increments PC depends on the nature of the instruction, for one byte instruction it increments PC by one, for two byte instruction it increments PC by two and for three byte instruction it increments PC by three such that PC always points to the address of the next instruction. 2 Stack Pointer (SP): the stack pointer is a reserved area of the memory in the RAM where temporary information may be stored. A 16 bit stack pointer is used to hold the address of the most recent stack entry. Main Slide 9 / 20
- 10. ALU of 8085 1 The 8085’s ALU performs arithmetic and logical operations on 8 bit variables. The arithmetic unit performs bitwise fundamental arithmetic operations such as addition and subtraction. The logic unit performs logical operations such as complement, AND, OR and EX - OR, as well as rotate and clear. The ALU also looks after the branching decisions. Main Slide 10 / 20
- 11. Instruction Decoder 1 The processor first fetches the opcode of instruction from memory and stores this opcode in the instruction register. It is then sent to the instruction decoder. The instruction decoder decodes it and accordingly gives the timing and control signals which controls the register, the data buffers, ALU and external peripherals signals depending on the nature of the instruction. Main Slide 11 / 20
- 12. Address Buffer 1 This is an 8 - bit unidirectional buffer. It is used to drive external high order address bus (A15 - A8). It is also used to tri - state the high order address bus under certain conditions such as reset, hold, halt and when address lines are not in use. Main Slide 12 / 20
- 13. Address/data Buffer 1 This is an 8 - bit bidirectional buffer. It is used to drive multiplexed address / data bus, i.e. low order addresses bus (A7 - A0) and data bus (D7 - D0). It is also used to tri - state the multiplexed address / data bus under certain conditions such as reset, hold, halt and when the bus is not in use. Main Slide 13 / 20
- 14. Increment / decrement address latch 1 This 16 - bit register is used to increment or decrement the contents of PC or stack pointer as a part of execution of instruction related to them. Main Slide 14 / 20
- 15. Interrupt control 1 The processor fetches, decodes and executes instruction in a sequence. Sometimes it is necessary to have processor the automatically executes one of a collection of special routines whenever special conditions exists within a program or the microcomputer system. 2 The most important thing is that, after execution of the special routine, the program control must be transferred to the program which processor was executing before the occurrence of the special condition. The occurrence of the special condition is referred as interrupt. 3 The interrupt control block has five interrupt inputs RST 5.5, RST 6.5, RST 7.5, TRAP and INTR and one acknowledge signal INTA. Main Slide 15 / 20
- 16. Serial input / output control 1 In situations like, data transmission over long distance and communication with cassette tapes or a CRT terminal it is necessary to transmit data bit by bit to reduce the cost of cabling. In serial communication one bit is transferred at a time over a single line. The 8085’s serial I/O control provides two lines, SOD and SID for serial communication. The serial output data (SOD) line is used to send data serially and serial input data (SID) line is used to receive data serially. Main Slide 16 / 20
- 17. Timing and control circuitry 1 The control circuitry in the processor 8085 is responsible for all operations. The control circuitry and hence the operations in 8085 are synchronized with the help of clock signal. Along with the control of fetching and decoding operations and generating appropriate signals for the instruction executions control circuitry also generates signals required to interface external devices to the processor 8085. Main Slide 17 / 20
- 18. Pin configuration of 8085 Main Slide 18 / 20
- 19. Control & Status signal Main Slide 19 / 20
- 20. Thank you Please send your feedback at nbahadure@gmail.com For more details and updates kindly visit https://sites.google.com/site/nileshbbahadure/home Main Slide 20 / 20