2. • Presented by:
PRATIK DATTA Roll no-10900311051
REEVU PAL Roll no-10900311070
PRATIP GHOSH Roll no-10900311052
RANADIP SAHA Roll no-10900311069
3. WHAT IS A MICROPROCESSOR
A microprocessor is a multipurpose, programmable electronic device that
accepts binary data as input ,processes the data and provides results as
output.
It works in tandem with the storage memory containing data and
instructions along with control unit, input and output devices amd forms
a microcomputer.
Every microprocessor recognizes and processes ‘n’ number of binary
digits(bits) at time and is known as the word length.It may vary from 4-
bit to 64-bit.
MICROPROCESSOR
3
ALU REGISTE
R
ARRAY
CONTROL UNIT
INPUT/OUTPUT
MEMORY
SYSTEM BUS
Slide # 1of 26
4. 8085- AN INTRODUCTION
The 8085 is an 8-bit general purpose microprocessor
that can address 64K Byte of memory.
It has 40 pins and uses +5V for power. It can run at a
maximum frequency of 3 MHz.
The pins on the chip can be grouped into 6 groups:
Address Bus.
Data Bus.
Control and Status Signals.
Power supply and frequency.
Externally Initiated Signals.
Serial I/O ports
Slide # 2 of 26
6. THE ADDRESS AND DATA BUSES
The address bus has 8 signal lines A8 – A15 which are
unidirectional.
The other 8 address bits are multiplexed (time shared) with
the 8 data bits.
So,the bits AD0 – AD7 are bi-directional and serve as A0 – A7
and D0 – D7 at the same time.
In order to separate the address from the data, we can use a
latch to save the value before the function of the bits
changes.
Slide # 4 of 26
7. DEMULTIPLEXING AD7-AD0
The basic requirement of demultiplexing is to save the total 16bit
address for the entire duration of execution of an instruction.
To make sure we have the entire address for the full three clock
cycles, we will use an external latch to save the value of AD7– AD0
when it is carrying the address bits. We use the ALE signal ,which
is kept high to enable this latch.
Then when ALE goes low, the address is saved and the AD7– AD0
lines carry the data bits D7-D0.
8085
ALE
A15-A8
Latch
AD7-AD0 A7- A0
D7- D0
Slide # 5 of 26
8. THE CONTROL AND STATUS SIGNALS
There are 4 main control and status signals. These are:
ALE : Address Latch Enable. This signal is a pulse that
become 1 when the AD0 – AD7 lines have an address on them.
It becomes 0 after that.
RD : Read- Active low,signifying ‘read’ operation
WR : Write- Active low,signifying ‘write’ operation.
IO/𝑀 : This signal specifies whether the operation is a
memory operation (IO/𝑀=0) or an I/O operation (IO/𝑀=1).
S1 and S0 : Status signals to specify the kind of operation
being performed
Slide # 6 of 26
9. CLOCK SIGNALS AND PINS
• 8085 MPU has 3 pins that
control or present the clock signal.
• X1 and X2 pins determine
the clock frequency.
• CLK OUT is a square-wave
output clock.
• The CLOCK OUT is one-half
the crystal frequency.
8085A
X1 CLK OUT
X2
6 MHz
Slide # 7 of 26
10. INTERRUPT AND EXTERNALLY INITIATED
SIGNALS
• INTR and 𝐼𝑁𝑇𝐴 are general purpose interrupts,the former being an
input signal from peripherals and later being output to the
corresponding source.
• RST 7.5,6.5,5.5 are vectored interrupts that transfer the
program control to specified memory locations.The priority order
is 7.5>6.5>5.5.
• TRAP is a Non-maskable interrupt that has the highest priority.
• HOLD , READY(Input) and HLDA are used for communication with
other devices and peripherals.
Slide # 8 of 26
11. BLOCK DIAGRAM OF 8085
MICROPROCESSOR
INTERRUPT CONTROL SERIAL I/O CONTROL
ACCUMULAT
OR
TEMP.
REGISTE
RS
TIMING AND CONTROL UNIT
INSTRUCTI
ON
REGISTERS
INSTRUCTION
DECODER &
MACHINE
CYCLE
ENCODING
ADDRESS(HIG
H) BUFFER
ADDRESS(LO
W)/DATA
BUFFER
B
Register
C
Register
D
Register
E
Register
H
Register
L
Register
Stack Pointer
Program Counter
+5
VGN
D X1
X2
CLK
OUT
READ
Y
𝑅𝐷
AL
E
S
0
S1
HLDA 𝑅𝐸𝑆𝐸𝑇 𝐼𝑁
RESET
OUT
𝑊𝑅 IO/𝑀 HOLD
8 BIT INTERNAL REGISTER
REGISTER
ARRAY
SID SO
D
RST 7.5
RST
5.5
TRA
P
INT
R
𝐼𝑁𝑇𝐴
FLAG FLIP-
FLOPS
ARITHMETI
C
LOGIC
UNIT
RST
6.5
Slide # 9 of 26
12. PROGRAMMING MODEL OF
8085
Accumulator:
It is 8 bit general purpose
register connected to ALU.
Performs arithmetic and logical
operations.
Result of an operation is stored
in accumulator
Temporary register:
All the arithmetic and logical
operations are done in the
temporary register but user can’t
access it.
It is not available for user.
Accumulator
ALU
Flags
Instruction
Decoder
Register
Array
Memory
Pointer
Registers
Timing and Control Unit
16-bit Address
Bus
8-bit Data
Bus
Control Bus
Slide # 10 of
26
13. FLAG REGISTERS
Flag Register: It is a group of 5 flip flops used to know status
of various operations done and is given by:
S: Sign flag is set when result of an operation is negative.
Z: Zero flag is set when result of an operation is 0.
AC: Auxiliary carry flag is set when there is a carry out of
lower nibble or lower four bits of the operation.
CY: Carry flag is set when there is carry generated by an
operation.
P: Parity flag is set when result contains even number of 1’s.
Rest(X) are don’t care flip flops.
8085 uses these flags in decision-making process.
S Z X AC X P X CY
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26
14. INSTRUCTION SET OF 8085
An instruction is a binary pattern designed inside a
microprocessor to perform a specific function.
8085 has 246 instructions.
Each instruction is represented by an 8-bit binary value.
These 8-bits of binary value is called Op-Code or
Instruction Byte.
8085 instructions can be classified as:
1. Data Transfer (Copy)
2. Arithmetic
3. Logical and Bit manipulation
4. Branch
5. Machine Control
Slide # 12 of
26
15. DATA TRANSFER (COPY) OPERATIONS
These instructions move data between registers, or between memory and
registers, from source to destination.
Before Instructions After Instructions
Load a 8-bit number 4F in register B:MVI B, 4FH B B
Copy from Register B to Register A:MOV A,B A A
B B
Load a 16-bit number 2050 in H H
Register pair HL:LXI H, 2050H L L
Copy from Register B to H H
Memory Address 2050 Containing data 9FH:MOV M,B L L
B B
XX 4FH
XX
4FH4FH
4FH
XX
XX
20H
50H
20
50
20
50
XX 9FH
Slide # 14 of
26
16. ARITHMETIC OPERATIONS / INSTRUCTIONS
These instructions perform the operations like: Addition, Subtraction, Increment
Decrement , etc.
Before Instructions After Instructions
Add a 8-bit number 32H to Accumulator: ADI 09H A A
Data
Add contents of Register B to Accumulator: ADD B A A
B B
Subtract a 8-bit no.32H from Accumulator: SUI 32H
Subtract contents of Register C from Accumulator: SUB C
Increment the contents of Register D by 1: INR D D D
Decrement the contents of Register E by 1: DCR E E E
07H
09H
10H
07H
09H
10H
09H
FFH 00H
FFH
FEH
Slide # 15 of
26
17. LOGICAL & BIT MANIPULATION OPERATIONS
1. Logically AND Register H with Accumulator: ANA H
2. Logically OR Register L with Accumulator: ORA L
3. Logically XOR Register B with Accumulator: XRA B
4. Compare contents of Register C with Accumulator: CMP C
5. Complement Accumulator: CMA
6. Rotate Accumulator Left: RAL
Slide # 16 of
26
18. BRANCHING OPERATIONS
These operations are used to control the flow of program execution
1. Jump to a 16-bit Address 2080H if Carry flag is SET: JC 2080H
2. Unconditional Jump: JMP 2050H
3. Call a subroutine with its 16-bit Address: CALL 3050H
4. Return back from the Call: RET
5. Call a subroutine with its 16-bit Address if Carry flag is RESET: CNC 3050H
6. Return if Zero flag is SET: RZ
MACHINE CONTROL INSTRUCTIONS
1. Stop program execution: HLT
2. Do not perform any operation: NOP
Slide # 17 of
26
20. STACK AND SUBROUTINES
• The Stack is a set of Memory locations ,either specified by the user or is
allotted by default , which stores information bytes temporarily.
• Say, If stack pointer is loaded with 2099H,the storing of bytes begins at 2098H and
continues in decreasing order such as 2098H,2097H etc.
• Instruction ‘PUSH’ is used to store data bytes(two at a time) on the stack and
‘POP’ is used to retrieve data back to the respective registers.
• EG: LXI SP,2099H
LXI D,42F2H
PUSH D
POP B
• Subroutine is a group of instructions
written separately to perform a function
which occurs repeatedly in the main program.
• ‘CALL’ is used to transfer execution
to specified address and ‘RET’ is
used to resume main program execution.
MEMORY
MEM
ADDRE
SS
F2 2097
42 2098
XX 2099
D 42 F2 E
B 42
C F2
PUS
H
PO
P
Slide # 19 of
26
21. COUNTERS AND DELAY
• A counter is designed by loading a number into one of the registers and
using INR/DCR/INX/DCX instructions.
• A loop is established to update the count and checking is done through
JNZ/JZ instructions whether or not to continue the loop.
• For a certain clock period, depending upon the No. of T-states of
instructions, every count generates a different time delay.
• Eg.: MVI C,FFH
LOOP: DCR C
JNZ LOOP
MVI takes 7 T-states , JNZ takes 10.Hence for a clock period of 0.5µsec,
the loop continues for 255(FFH) times and a delay of 1.8ms is generated.
• For larger amount of delay , a Register pair as well as a loop within
loop techniques can be used to achieve the required delay.
Slide # 20 of
26
22. MICROPROCESSOR BASED TRAFFIC CONTROL
SYSTEM
The Basic Objective is to design a Traffic control System with a
provided on/off time to three traffic lights-GREEN, YELLOW and
RED.
This is done by using 8255 peripheral interface which can be
programmed to transfer data under given conditions.
Fig. shows the interfacing diagram to control 12 LED’s.
Port A is used to control lights on N-S road
and Port B is used to control lights on W-E road.
For understanding the basic application of 8085
here we have demonstrated only for North-South
and East-West movement only. Further development
can be done once the basic procedure is understood
22
Slide # 21 of
26
23. SOFTWARE FOR TRAFFIC LIGHT
CONTROL
• Control word for Initialisation of 8255: 80H
I/O Mode Port A in Mode0 Port A=Output Port B in Mode0 Port B=Output
• Data bytes to be sent for specific combination
Similarly to glow Y1 and Y2 Port A output=12H , Y3 and Y4 Port B
output=12H.
To glow R3 and R4 Port A output=09H , G1 and G2 Port B
output=24H.
IO/BSR MODE A PORT A PORT C
H
MODE B PORT B PORT C
L
1 0 0 0 X 0 0 X
TO
GLOW
P
A
7
P
A
6
PA
5
P
A
4
P
A
3
P
A
2
PA
1
P
A
0
PORT
A
OUTP
UT
P
B
7
P
B
6
PB
5
PB
4
PB
3
PB
2
PB
1
PB
0
PORT
B
OUTPU
T
R1,R2,
G3,G4
X X 1 0 0 1 0 0 24H X X 0 0 1 0 0 1 09H
Slide # 22 of
26
24. FLOW CHART FOR PROGRAM EXECUTION
Address of Control Register=83H
Data for port A=24H,port B=09H
Delay Generated= 10sec
Data for port A=12H,Port B=12H
Delay generated=03 sec
Send Data to Port
A,B to glow
R1,R2,G3,G4
Call Delay
subroutine using
count of 14H
Send Data to Port
A,B to glow
Y1,Y2,Y3,Y4
24
Slide # 23 of
26
Initialize Port A,B
of 8255 in output
mode
Call Delay
subroutin
e using
count of
06H
25. Send Data to Port
A,B to glow
R3,R4,G1,G2
Data for Port A=09H,Port
B=24H
Call Delay
Subroutine using
count of 14H
Send Data to Port
A,B to glow
Y1,Y2,Y3,Y4
Delay generated=10 sec
Data for Port A=12H,Port
B=12H
Call Delay
Subroutine using
count of 06H
Delay Generated=06 sec
Use Unconditional Jump to
starting
address: JMP START 25
Slide # 24 of
26
Return to start
and continue the
process
26. CONCLUSION
The 8085 processor was used in a few early personal computers,
produced from1977 to early-to-mid-1980’s.
Now-a-days, in many engineering schools the 8085 processor is
used in introductory microprocessor courses.
However with time, better quality microprocessors have been
developed with greater bit processing capability(32 and 64 bit )
along with huge no of other modifications
Slide # 25 of
26
27. REFERENCES AND BIBLIOGRAPHY
• BOOKS:
• Microprocessor Architecture, Programming and Applications with the
8085 by Ramesh Gaonkar.
• Fundamentals of Microprocessors and Microcontroller by B.Ram .
• INTERNET:
• http://en.wikipedia.org/wiki/Intel_8085
• http://www.nptel.ac.in/courses/Webcourse-contents/IISc-
BANG/Microprocessors and Microcontrollers
• http://instrumentationandcontrollers.blogspot.in/2011/01/microproce
ssor-based-traffic-light.html
Slide # 26 of
26
