Dept. of Electronics A. N. College, Patna M. Sc Dept. of Electronics A. N. College, Patna M. Sc. (Previous) Paper -V Microprocessor & its Applications Prepared by- S. P. Vats Dept. of Electronics, A. N. College, Patna

Module Contents The curriculum consists of 5 modules with 8085 as the main microprocessor Introduction 8085 pins and their applications 8085 Architecture & Programming 8085 Interfacing Techniques Introduction to other 8-bit microprocessors Z80, MC6800

Module I- Introduction A microprocessor is the main component of a microcomputer system and is also called as CPU (Central Processing Unit). This module is designed to give introduction to some elementary terms related to a microcomputer system. The topics covered are: Microprocessor as CPU Hardware and Software Input & Output Devices Memories

Module II- 8085 Pins For complete understanding of the interfacing circuits of memory, I/O devices etc. to the 8085 CPU it is required to learn about the functions of all the pins of 8085. The pins of 8085 are classified in following groups: Address and Data pins Control & status pins Interrupt pins Serial I/O pins Clock pins Reset pins DMA pins Power supply pins

Module III- 8085 Architecture To develop programs for 8085, it is required to completely understand the internal functional blocks of 8085. 8085 architecture includes following functional blocks: 8085 Registers Timing and control unit ALU Interrupt control unit Serial I/O control unit Instruction decoder & encoder unit

Module III- Programming the 8085 Programming of 8085 requires complete knowledge of the instruction set and its structure. This requires study of- 8085 Instruction set 8085 addressing modes One, two & three bytes instruction Programming examples

Module IV- Interfacing Techniques A microcomputer system consist of a minimum of memory & I/O devices. To connect these devices properly with 8085 is referred to as interfacing. This module provides interfacing techniques for- RAM & ROM I/O devices Special purpose programmable devices such as 8255, 8253/8254, 8257, 8259

Module V-Introduction to other 8-bit microprocessors This module is designed to develop an introductory knowledge about some other 8-bit microprocessors used in embedded technology. The microprocessors covered in this module are: Z80 of Zilog MC6800 of Motorola Corporation

Module I Introduction: Microcomputer & Microprocessor A microcomputer is a programmable machine. Modern computers are electronic and digital. The two principal characteristics of a computer are: It responds to a specific set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a program) Its main components are CPU Input & Output devices memory A microprocessor is a programmable VLSI chip which controls and performs all operations in a microcomputer. Its main units are- ALU Registers Control Unit

Block diagrams (Microcomputer & Microprocessor)

Hardware All general-purpose computers require the following hardware components: Memory: Enables a computer to store data and programs. Mass storage device: Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives. Input device: Usually a keyboard and mouse are the input device through which data and instructions enter a computer. Output device: A display screen, printer, or other device that lets you see what the computer has accomplished. Central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.

Software The programs and data stored in a microcomputer is called as software. Programs can be written in low level languages or high level languages. A low level language can be binary language or assembly language. A CPU recognizes only binary language which is called as machine language. Assembly language instructions contain alphabets and/or numeric characters. To run assembly language programs a converter called as assembler is required. High level languages are more user friendly and contain simple words of English language. To run high level programs, converters such as compilers or interpreters are required.

Input & Output Devices Input devices are used to input electrical or physical information in a microcomputer system in digital form. In embedded applications, commonly used input devices are simple switches and sensors. In general purpose microcomputers, input devices can be keyboards, scanners, mouse etc. Output devices are used to display or perform required operation. In embedded applications commonly used output devices are LED display units, LCD display units, stepper motors etc. In general purpose computers output devices are mainly CRTs, LCD screens, LED screens, Printers etc.

Memories Memory in a microcomputer system is used to store data and programs temporarily or permanently. The memories of primary concern for the CPU are only RAM & ROM which are called as primary memory or main memory. The CPU, at any time, only communicates with RAM & ROM. Other than primary memories, there are also secondary memories which are used for mass storage of data and programs and are transferred to the primary memory when required to be executed by the CPU. Examples of secondary memories are Hard Disks, Floppy Disks, DVDs, flash drives etc.

Memory Classification

Module II- 8085 pins

Pin description Higher Order Address pins- A15 – A8 Lower Order Address/ Data Pins- AD7-AD0 These are time multiplexed pins and are de-multiplexed using the pin ALE Control Pins – RD, WR These are active low Read & Write pins Status Pins – ALE, IO/M (active low), S1, S0 ALE (Address Latch Enable)-Used to de-multiplex AD7-AD0 IO/M – Used to select I/O or Memory operation S1,S0 – Denote the status of data on data bus Interrupt Pins – TRAP, RST7.5, RST 6.5, RST 5.5, INTR, INTA These are hardware interrupts used to initiate an interrupt service routine stored at predefined locations of the system memory. Serial I/O pins – SID (Serial Input Data), SOD (Serial Output Data) These pins are used to interface 8085 with a serial device.

Pin Description Contd. Clock Pins- X1, X2, CLK(OUT) X1, X2- These are clock input pins. A crystal is connected between these pins such that fcrystal= 2f8085 where fcrystal= crystal frequency & f8085 = operating frequency of 8085 CLK(OUT) – This is an auxiliary clock output source Reset Pins – Reset In (active low), Reset Out Reset In is used to reset 8085 whereas Reset Out can be used to reset other devices in the system DMA (Direct Memory Access) pins – HOLD, HLDA These pins are used when data transfer is to be performed directly between an external device and the main memory of the system. Power Supply Pins - +VCC, VSS

Module III – 8085 Architecture

8085 Architecture Contd.. The Registers are of 8-bit & 16-bit size used for different purposes A- Accumulator – This is an special purpose register. All the ALU operations are performed with reference to the contents of Accumulator. B,C,D,E,H,L – General purpose registers. These registers can also be used for 16-bit operations in pairs. The default pairs are BC, DE & HL. F – Flag register – This register indicates the status of the ALU operation. PC – Program Counter – This is a 16-bit register used to address the memory location from where an instruction is going to be executed. SP – Stack pointer - This is a 16-bit register used to address the top of the stack memory location. Temporary register, W & Z – These registers are only used by 8085 and are not available for the programmer.

8085 Architecture Contd.. ALU – Arithmetic & Logic Unit ALU of 8085 performs 8-bit arithmetic & logical operations. The operations are generally performed with Accumulator as one of the operands. The result is saved in accumulator register. Timing & Control Unit This unit works as the brain of the CPU and generates all the timing and control signals to perform all the internal & external operations of the CPU. Instruction Decoder & Machine Cycle Encoder Unit This unit decodes the op-code stored in the Instruction Register (IR) and encodes it for the timing & control unit to perform the execution of the instruction.

Instruction Set Instruction set of 8085 can be classified in following groups: Data Transfer Instructions These instructions can perform data transfer operations between Registers of 8085 e.g. MOV 8085 registers and main memory e.g. LDA, STA, MOV, LDAX, STAX, MVI, LXI etc. Accumulator register and I/O devices e.g. IN, OUT Data transfer instructions never affect the flag bits

Instruction Set Contd.. Arithmetic Instructions Logical Instructions 8085 can perform only 8-bit addition, subtraction and compare operations. These operations are always performed with accumulator as one of the operands. The status of the result can be verified by the contents of the flag register. Op-codes for arithmetic instructions include ADD, ADI, ADC, ACI, SUB, SUI, SBB, SBI, CMP, CPI Logical Instructions 8085 can perform 8-bit basic logical operations -AND, OR, XOR, NOT with some special operations such as rotate and shift operations Logical instructions also modify the flag bits. Op-codes for logical instructions include ANA, ANI, ORA, ORI, XRA, XRI, CMA, RAL, RLC, RAR, RRC etc.

Program Control Instructions Instruction Set Contd.. Program Control Instructions These instructions are used to transfer the program control: to jump from one memory location to any other memory location within a program from one program to another program called as a subroutine 8085 Instruction set consists of following program control instructions: Jump Instructions Call & Return Instructions Restart instructions

Program control instructions Instruction Set Contd.. Program control instructions Unconditional or Conditional Unconditional program control instructions perform branching operation unconditionally Conditional program control instructions perform branching operation with reference to the condition of flag bits.

Conditional Program control instructions are Instruction Set Contd.. Unconditional Program control instructions are JMP Call & RET RST n (n=0-7) Conditional Program control instructions are JNC, JC, JNZ, JZ, JP, JM, JPE, JPO CNC, CC, CNZ, CZ, CP, CM, CPE, CPO RNC, RC, RNZ, RZ, RP, RM, RPE, RPO

Machine control Instructions Instruction Set Contd.. Machine control Instructions These instructions include special instructions such as HLT – To halt the CPU NOP – To perform no operation SIM – To set the masking of hardware interrupts and serial output data RIM – To read the status of interrupt mask and serial input data EI – Enable Interrupt DI – Disable Interrupt

Programming of 8085 The following link can be used to access different type of programs. Lab Manual The programs can be loaded and verified in the 8085 based microcomputer system available in the microprocessor lab

Addressing Modes 8085 instructions can be classified in following addressing modes Register Addressing mode Instructions which have their operands in registers only e.g. MOV, ADD, SUB, ANA, ORA, XRA etc. Immediate Addressing mode Instructions in which operand immediately follows the op-code e.g. MVI, LXI, ADI, SUI, ANI, ORI etc. Direct Addressing mode Instructions have their operands in memory and the 16-bit memory address is specified in the instruction e.g. LDA, STA, LHLD, SHLD etc.

Addressing Modes Contd.. Register Indirect Addressing mode Instructions have their operand in memory and the 16-bit memory address is specified in a register pair e.g. LDAX, STAX, PUSH, POP etc. Implicit Addressing mode These instruction have their operand implied in the op-code itself e.g. CMA, CMC, STC etc.

Instruction size An instruction is assembled in the memory of a microcomputer system in binary form. The size of an instruction signifies how much memory space is required to load an instruction in the memory. 8085 instructions are of following sizes: One-byte Instructions e.g. MOV, ADD, ANA, SUB, ORA etc. Two-byte instructions e.g. MVI, ADI, ANI, ORI, XRI etc. Three-byte instructions e.g. LXI, LDA, STA, LHLD, SHLD etc.

Module IV: Interfacing Techniques Memory Interfacing 8085 uses 16-bit memory addressing system allowing a maximum of 64 KB size of memory The logical memory address range is 0000h-FFFFh These 64k addresses can be allotted separately to RAMs & ROMs Some interfacing circuit examples can be found in the following link Interfacing Examples

Interfacing Contd.. I/O Interfacing To interface Input Devices Octal buffers are used. These octal buffers are called as input ports Octal buffers contain a set of eight buffers for an 8-bit system data bus A buffer is basically a current amplifier which amplifies the smaller magnitude currents of input devices before being supplied to the CPU The tri-state logic also provides the addressing and control logic for the CPU

Interfacing Contd.. To interface output devices Octal Latches are used. A latch is basically a D Flip-Flop Latches are used to hold the output data because information on system data bus is available for a very small duration of time. I/O interfacing techniques

I/O structure of 8085

Interfacing Contd.. There are three major types of data transfer between the microcomputer and art I/O device. They are- Programmed I/O : In programmed I/O the data transfer is accomplished through an I/O port and controlled by software. Interrupt driven I/O : In interrupt driven I/O, the I/O device will interrupt the processor, and initiate data transfer. Direct memory access (DMA) : In DMA, the data transfer between memory and I/O can be performed by bypassing the microprocessor.

Interfacing Contd.. Some special purpose programmable devices used with 8085 are listed in the table of next slide. These devices are used in the system according to the requirement.

Interfacing Contd..

Interfacing Contd..