notes

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Block diagrams
(Microcomputer & Microprocessor)

11. 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.

12. 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.

13. 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.

14. 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.

15. Memory Classification

16. Module II-
8085 pins

17. 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.

18. 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

19. Module III –
8085 Architecture

20. 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.

21. 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.

22. 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

23. Instruction Set Contd..
 Arithmetic 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.

24. 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

25. 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.

26. 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

27. 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

28. 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

29. 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.

30. 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.

31. 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.

32. 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

33. 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

34. 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

35. I/O structure of 8085

36. 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.

37. 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.

38. Interfacing Contd..

39. Interfacing Contd..