WORKING OF MICRO-PROCESSOR SOME MORE DEEPLY

* address bus is a uni-directional bus
from micro-processor to peripheral >>16 bit width

* data bus: bi-directional

# 8 bit AD0-AD7
# 2^8 peripherals

* control bus


# MEMR==memory read
# MEMW==memory write
# IOR==input output read
# IOW==input output write

***control bus compared of various single lines that carries synchronization signals . the micro-processor use this lines to provide timing signals

the micro-processor generate specific controller signals for every operations. it performs , such as memory read or input/output write

these signals are used to identified a device time with which micro-processor intense to communicate


** general purpose register:::store data during programe execution.this register are accessible by the user. or it is programmable. B,C,D,E,H,L register .they are 8 bit register.
accumulator also 8 bit register

** stack pointer & program counter are 16 bit register
**if there is a need of 16 bit operation. they can pair. that means they can pair as BC,DE, HL total 8+8 = 16 bit( BL like pairing not possible)

.................................................................................................**FLAG REGISTER**


.............................................................................................













# C - carry flag
# P - parity flag
# AC - auxiliary carry flag
# Z - zero flag
# S - sign flag

****************flag register also 8-bit register***************

5 flip - flop that set or reset according to the result of the arithmetic operation perform by ALU

** CARRY FLAG**

during the addition of two number . if they have sum in accumulator is greater than 8-bit . the flip-flop used to indicate the carry is set to one otherwise reset

** PARITY FLAG**

after the arithmetic operation if the result have been even number of one then the parity flag set.for odd number of one then the parity flag reset.

** AUXILIARY CARRY FLAG**

in an arithmetic operation , when a carry is given by 3rdbit and passed on 4thbit. the AC flag will set.
for example : 1001 1100 and 1000 1001
1001 1100
1001 1001
......................
10011 0101
here position 1 and 1( 1001 1100 and 1001 1001) when we find sum there is sum=0 and carry = 1. then carry goto 3 rd bit to 4 th bit. then auxiliary carry flag set . equal=1.blue color 1 is present then carry flag set equal=1.

** ZERO FLAG**

after the arithmetic operation if the result is ZERO then the zero flag will set

** SIGN FLAG**

after the arithmetic operation if the last bit is one ( bit D7 result is one ) sign flag will set . equal= 1.

more ex: 1010 0010
0101 1110
..................
10000 0000

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**PROGRAM COUNTER**
......................................................

it is 16 bit register also memory pointer, micro-processor use this register to sequence the execution of instruction , the function of PROGRAM COUNTER is to point the memory address from which next bytes is to be fetch
when a bytes is being fetched program counter is incremented by one to point to the next memory location

#########################

**STACK POINTER**
.......................................................
stack pointer is also 16 bit register use as a memory pointer it points to the memory location in the read,write memory called stacks. beginning
of the stack is defined by loading a 16 bit address to the stack pointer

###########################

**INSTRUCTION REGISTER **
..........................................................


IR hold op-code of the current instruction.

###########################

**TEMPORARY REGISTER **
.........................................................
temporary register are 8 bit register associated with ALU. which hold data during arithmetic or logic operation . this register used by micro-processor and not accessibly by the user

DETAILS 8085 MICRO-PROCESSOR PIN DIAGRAM

X1 and X2: are clock input pin. Crystal oscillator connected to these two pin

RESET OUT: indicate that micro-processor RESET. This signal can be used to RESET other devices

SID (sid in diagram. my mistake): SERIAL INPUT DATA is input pin used to accept serial one bit data

SOD: SERIAL OUTPUT DATA pin used to send serial 1 bit data

TRAP: it is an EDGE triggered highest priority non maskable interrupt

RST 7.5,RST 6.5,RST 5.5 : these are markable interrupt and have low priority than TRAP

Priority is in the order 7.5>6.5>5.5

INTR and INTA: INTR is a interrupt request signal after which micro-processor generate INTA or interrupt acknowledge signal

AD0-AD7: address data multiplexer bus

A8-A15: tri-state higher order address line

Tri state means it have 3 terminal one normal input and normal out put and one high impedance state . so we can control the output effectively . if there is high impedance state circuit act as a open circuit

IO/M(m bar) : this is output pin or signal used to indicate used to whether 8085 is working in I/O mode (IO/M( m bar)=1 , memory mode (IO/M( bar)=0.

READY: this is an output to check the status of output device. If it is low , the micro-processor will wait until it is high

RESET IN: this is input signal .when RESET IN is low micro-processor restart and starts executing from location 000H

ALE: address latch enable is output signal it goes high when operation is started by processor

SO, SI: these are the status signals used to indicates type of operations

RD: READ is active low input signal to read data from I/O devices or memory

WR : WRITE is an active low output signals used to write data on memory or I/O device

CLK (out) : it is the clock for users ,use for other digital circuits. It’s frequency is same as processor frequency

HOLD&HLDA: HOLD is on input signal this signal indicates that a peripherals requesting the use of address and data bus. In respond to hold micro-processor

Generates HLDA that is HOLD acknowledgement signal

VCC & VSS : power supplied to the micro-processor VCC positive supply And VSS is a negative supply

READY pin is used to communicate slow peripherals

When ALE is high it indicates that bits on AD0-AD7 pins address pin

Working details of S0 and S1

S0 and S1 indicates type of operations

IO/M (ACTIVE LOW)	S0	S1	DATA BUS STATUS(OUTPUT)
0	0	0	Halt(stop)
0	0	1	MEMORY WRITE
0	1	0	MEMORY READ
1	0	1	IO WRITE
1	1	0	IO READ
0	1	1	OP-CODE FETCH
1	1	1	INTERUPT ACKNOWLEDGE