TK 2633 Microprocessor

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TK 2633Microprocessor Interfacing

• Lecture 4 Introduction to 8085 Instruction Set
  (1)

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INTRODUCTION

• A microcomputer performs a task by reading and
  executing the set of instructions written in its
  memory.
• This set of instructions, written in a sequence,
  is called a program.
• Each instruction in the program is a command, in
  binary, to the microprocessor to perform an
  operation.

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MACHINE CONTROL OPERATIONS
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DATA TRANSFER OPERATIONS

• The data transfer instructions copy data from a
  source into a destination without modifying the
  contents of the source.
• The previous contents of the destination are
  replaced by the contents of the source.

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DATA TRANSFER OPERATIONS
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EXAMPLE 1
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EXAMPLE 2

• Load the accumulator A with the data byte 82H
  (the letter H indicates hexadecimal number), and
  save the data in register B.

Instructions MVI A, 82H, MOV B,A
The first instruction is a 2-byte instruction
that loads the accumulator with the data byte
82H, and the second instruction MOV B,A copies
the contents of the accumulator in register B
without changing the contents of the accumulator.
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EXAMPLE 3

• Write instructions to read 8 ON/OFF switches
  connected to the input port with the address OOH,
  and turn on the devices connected to the output
  port with the address 01H, as shown in Figure
  6.1.

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SOLUTION FOR EXAMPLE 3

• The input has eight switches that are connected
  to the data bus through the tri-state buffer.
• Any one of the switches can be connected to 5 V
  (logic 1) or to ground (logic 0),
• and each switch controls the corresponding device
  at the output port.
• The microprocessor needs to read the bit pattern
  on the switches and send the same bit pattern to
  the output port to turn on the corresponding
  devices.

Instructions IN OOH OUT 01H HLT

• When MPU executes the instruction IN 00H, it
  enables the tri-state buffer.
• The bit pattern 4FH formed by the switch
  positions is placed on the data bus and
  transferred to the accumulator (reading an input
  port).
• When MPU executes OUT 01H,
• it places the contents of the accumulator on the
  data bus and enables the output port O1H (writing
  to output port).
• The output port latches the bit pattern and turns
  ON/OFF the devices connected to the port
  according to the bit pattern.

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Illustrative Program Data Transfer

• PROBLEM STATEMENT
• Load the hexadecimal number 37H in register B,
  and display the number at the output port labeled
  PORT1.
• PROBLEM ANALYSIS
• Step 1 Load register B with a number.
• Step 2 Send the number to the output port.
• QUESTIONS TO BE ASKED
• Is there an instruction to load the register B?
  YESMVI B.
• Is there an instruction to send the data from
  register B to the output port? NO. Review the
  instruction OUT. This instruction sends data from
  the accumulator to an output port.
• The solution appears to be as follows Copy the
  number from register B into accumulator A.
• Is there an instruction to copy data from one
  register to another register? YESMOV Rd,Rs.

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Illustrative Program Data Transfer

• FLOWCHART
• Generally, a flowchart is used for two purposes
• to assist and clarify the thinking process
• and to communicate the programmers thoughts or
  logic to others.

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Illustrative Program Data Transfer
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Illustrative Program Data Transfer
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Illustrative Program Data Transfer
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Exercises

• Write instructions to read the data at input PORT
  07H and at PORT 08H. Display the input data from
  PORT 07H at output PORT OOH, and store the input
  data from PORT 08H in register B.

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Move Immediate Instructions
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Move Immediate Instructions
The memory location, which is indirectly
addressed by the HL register pair, appears as the
letter M in all instructions.
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Direct Data Transfer Instructions

• Direct data transfer instructions are useful if
  only one byte or word of data is transferred to
  or from the memory.
• If more than one byte or word is transferred, it
  is more efficient to use indirectly addressed
  instruction.

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Direct Data Transfer Instructions
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Direct Data Transfer Instructions
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Direct Data Transfer Instructions
Copies the contents of location 1000H into the L
register and the contents of location 1001 H into
the H register
stores the contents of the L register at memory
location I200H and the H register at location
1201H
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INDIRECT DATA TRANSFER INSTRUCTIONS

• With register indirect addressing, a register
  pair holds the address of the memory location
  accessed by the instruction.
• The contents of the register pair indirectly
  addresses a memory location.
• Whenever, the letter M appears instead of a
  register, the HL register pair indirectly
  addresses a memory location.

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INDIRECT DATA TRANSFER INSTRUCTIONS
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INDIRECT DATA TRANSFER INSTRUCTIONS
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REGISTER DATA TRANSFER INSTRUCTIONS
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REGISTER DATA TRANSFER INSTRUCTIONS
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STACK DATA TRANSFER INSTRUCTIONS

• The Intel 8085A microprocessor has a LIFO
  (last-in, first-out) stack memory.
• The stack memory stores both return addresses
  from subroutines and data temporarily.
• The microprocessor cannot locate the stack memory
  when power is first applied to the system because
  the number in the SP is unknown.
• The location of the stack must be initialised
  after the application of system power.

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STACK DATA TRANSFER INSTRUCTIONS

• The programmer decides what portion of the
  read/write memory is to function as the stack,
  and then loads the SP with the top location plus
  one byte.
• The byte location above the stack is never used,
  but must be the initial value of the stack
  pointer.
• The SP always points to the current exit point.
• The stack is a LIFO stack.

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STACK DATA TRANSFER INSTRUCTIONS

• If data are pushed (placed) onto the stack, they
  move into the memory locations addressed by SP-1
  and SP-2.
• Note that pairs of registers always move to the
  stack.
• A PUSH instruction stores the high-order register
  first (SP - 1), followed by the low-order
  register (SP -2).
• The SP then decrements by two so that the next
  push occurs below the first.
• Notice that when the PUSH occurs, nothing is
  placed at the location addressed by the stack
  pointer.
• This is why the SP is initialised at one byte
  above the top of the stack.

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STACK DATA TRANSFER INSTRUCTIONS
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STACK DATA TRANSFER INSTRUCTIONS
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STACK DATA TRANSFER INSTRUCTIONS

• It is also important to note that PUSHes and POPs
  must occur in pairs
• one PUSH, one POP,
• two PUSHes, two POPs, and so on.

Note POP PSW will copy the data from location
pointed by SP into flag register and data from
(SP1) will copy into A. The SPSP2.
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MISCELLANEOUS DATA TRANSFER INSTRUQTIONS

• Exchange DE with HL (XCHG)
• The XCHG instruction exchanges the contents of
  the HL register pair with the contents of the DE
  register pair.
• Load SP from HL (SPHL)
• Is a one-byte instruction, copies the contents of
  the HL register pair into the SP.
• Exchange HL with Stack Data (XTHL)
• This instruction exchanges the contents of the HL
  pair with the most recent data on the stack.
• Input/Output Data Transfer Instructions
• IN instruction inputs data from an I/O device
  into the accumulator.
• OUT sends accumulator data out to an I/O device.

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SUMMARY

• Data transfer instructions transfer information
  from register to register, from register to
  memory, from memory to register.
• Data transfer instructions also allow data
  transfer between registers and stack or the I/O
  devices in a system.
• The Intel 8085A uses four different addressing
  modes direct, register, register indirect, and
  immediate.
• Direct addressing accesses a memory location to
  transfer data between memory and the accumulator
  or HL register pair. The address of the data
  follow with the instruction in the memory.
• Register addressing allows either a single 8-bit
  register (B, C, D, E, H, L, or A) or a 16-bit
  register pair (BC, DE, HL, and SP).
• Register indirect addressing allows the
  instruction to address memory through the address
  held in a register pair.

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SUMMARY

• Immediate addressing is used whenever the data (8
  or 16 bits) are a constant. Immediate data
  immediately follow the opcode in the program.
• The M register or operand indirectly addresses
  memory through the HL register pair.
• The LDA and STA instructions load or store the
  accumulator. The LHLD and SHLD instructions load
  or store the HL register pair.
• Besides M for indirectly addressing the memory,
  the DE and BC register pairs are also available.
  The LDAX and STAX instructions allow the
  accumulator to be indirectly stored or loaded
  from the memory by using the BC or DE register
  pairs.

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SUMMARY

• Register data transfer instructions are the most
  numerous form of data transfer 63 instructions.
• The stack memory is a LIFO (last-in, first-out)
  memory that stores data and return addresses from
  subroutines.
• The SP register indirectly addresses the stack.
  The stack functions with the stack data transfer
  instructions PUSH, POP, and XTHL.
• The PSW is the processor status word that
  contains both the accumulator and the flag byte.
  The accumulator is the high-order register and
  the flag bits are the low-order register.
• IN and OUT effect data transfers between an
  external I/O device and the accumulator.
• I/O devices are often called I/O ports and are
  addressed by an 8-bit I/O port address.

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Exercises

• Write a sequence of immediate instructions that
  store a 16H into memory location 1200H and a 17H
  in memory location 1202H.
• Write a sequence of instructions that use
  register indirect addressing to transfer the
  contents of A into location 2800H, B into 2801H,
  and C into 2802H.
• Write a sequence of instructions that use
  register indirect addressing to transfer the
  number stored in memory location 1300H into
  memory location 2302H.

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Thank youQA