Micro processor and micro controller lecture notes, Lecture notes of Microprocessors

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MICROPROCESSOR(μp)

UNIT -I

FEATURES OF 8085

1. It is an 8-bit microprocessor, i.e it can accept or provide

8-bit data simultaneously.

2. It operates on a single +5v power supply connected at

Vcc; power supply ground is connected to connected

Vss.

3. It operates on clock cycle with 50% duty cycle.

4. It can operate with a 3 MHz clock frequency.

5. It has 16 address lines ,hence it can access (2^16)

64Kbytes of memory.

6. It provides 8 bit I/O addresses to access (2^8) 256 I/O

ports.

Cont…..

9. The ALU of 8085 performs :

(a) 8-bit addition with or without carry

(b) 16-bit binary addition

(c) 2 digit addition

(d) 8- bit binary subtraction with or without

borrow

(e) 8 bit –logical AND,OR,Ex-

OR,complement(NOT) and bit shift operations.

10.It provides 5 hardware interrupts :TRAP, RST

7.5,6.5,5.5,and INTR

11.It has serial I/O control which allows serial

communication

Cont….

12.It provides control signals (IO/M,RD,WR) to control the bus cycles ,and hence external bus controller is not required 13.It has mechanism by which it is possible to increase its interrupt handling capacity 14.It can be used to implement three chip microcomputer with supporting I/O devices like IC 8155 and IC 8355

• ARCHITECTURE OF

Description:

1. It consists of various functional blocks as listed

below:

* Registers

* ALU

* Instruction Decoder and machine cycle

encoder

*Address Buffer

* Address/Data buffer

* Incrementer/Decrementer Address Latch

*Interrupt Control

*Serial I/O control

* Timing and Control Circuitry

Cont…..

 (^) 8085 Registers are classified as 1.General Purpose registers:

• B,C,D,E,H and L are 8-bit general purpose registers can be used as separate 8-bit registers or as 16-bit register pairs as BC,DE and HL.
• When used in register pair mode, the higher order byte reside in the first register (i.e. in B when BC is used as register pair ),and the lower order byte in the second (i.e. in C when BC is used as register pair)
• HL pair also functions as a data pointer or memory pointer. These are also called as scratchpad registers, as user can store data in them. 2.Temporary Registers :
• (a) Temporary Data Register:
• The ALU has 2 inputs, One input is supplied by the accumulator and the other one from Temporary Data Register
• The programmer cannot access this temporary data register
• However it is mostly used as execution of most arithmetic and logical operations

Cont……

 For example:  ADD B is the instruction in the arithmetic group of instructions which adds the contents of register A and register B and stores result in register A. The operation is performed by ALU .The ALU takes input from register A and temporary data register. The contents of B are transferred to  B)W and Z Registers:  W and Z are two 8-bit temporary registers of 8085 microprocessor, which is not accessible to the user.  They are exclusively used for the internal operation by the microprocessor.  These registers are used either to store 8-bit of information in each W and Z registers or a 16-bit data in W, Z register pair with lower order 8- bits in Z and higher-order 8-bits in W register.

Cont……

Similarly, in a logical operation involving two operands, one operand has to be in the accumulator. Also, some other operations, like complementing and decimal adjustment, can be performed only on the accumulator.  (b)Flag Register : It is a 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); as shown in

Cont….

S-Sign flag - After the execution of arithmetic or logical operations, if bit D7 of the result is 1, the sign flag is set. In a given byte if D7 is1, the number will be viewed as a negative number. If D7 is 0, the number will be considered as a positive number. Z-Zero flag -The zero flag sets if the result of the operation in ALU is zero and flag resets if the result is non zero. The zero flags are also set if a certain register content becomes zero following an increment or decrement operation of that register.

Addition 9BH -----> 1001 1011 +75 H -----> + 0111 0101

---

Carry 1 10 H -----> 1 0001 0000 Subtraction 89H -----> 1000 1001 -AB H -----> - 1010 1011

---

Borrow1 10 H -----> 1 1101 1110

Cont…..

 c) Instruction Register:  (^) ***** In a typical processor operation, the processor first fetches the opcode of instruction from memory (i.e. it places an address on the address bus and memory responds by placing the data stored at the specified address on the data bus).  (^) * The CPU stores this op code in a register called the instruction register. This op-code is further sent to the instruction decoder to select one of the 256 alternatives.

 Sixteen Bit Registers:

 (^) a) Program counter (PC) :  (^) * Program is a sequence of instructions.  (^) * 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.

Cont…

 Arithmetic and logical Unit:  (^) It is multi operational combinational logic circuit, same as IC 74181(ALU).It performs arithmetic and logical operations like AND ing, OR-ing, EX-OR-ing, ADDITON, SUBTRACTION, etc.  (^) It is not accessible by user.  (^) The word length of ALU depends upon of an internal data bus.  (^) It is 8 bit. It is always controlled by timing and control circuits.  (^) It provides status or result of flag register.  (^) Adder: It performs arithmetic operations like addition, subtraction, increment, decrement, etc. The result of operation is stored into accumulator.  (^) Shifter: It performs logical operations like rotate left, rotate right, etc. The result of operation is again stored into accumulator.

Cont….

 (^) Status Register: Also known as flag register. It contains a no. of flags either to indicate conditions arising after last ALU operation or to control certain operations.  (^) Instruction Decoder:  (^) It is an 8-bit register.  (^) When an instruction is fetched from memory then it is stored in the Instruction register.  (^) Instruction decoder decodes the information present in the Instruction register.  (^) Address Buffer:  (^) This is an 8-bit uni-directional buffer.  (^) It is used to drive external high order address bus(A15-A8).  (^) It is also used as to tri-state the high order under certain conditions such as reset, hold ,halt and when address lines are not in use.