Learn Microprocessor 8085 from beginner to advanced: interview questions, programming, architecture, and FAQs for students & embedded engineers.

If you ever wanted a simple, clear, and genuinely explanation of the Microprocessor 8085, this is your complete guide. Think of this as a friendly conversation where we go from basics to advanced topics without jargon or confusion.

Whether you’re a student preparing for your microprocessor exam, an engineer revising concepts, or someone exploring old-school tech out of curiosity, this Microprocessor 8085 complete guide covers everything.

What Is Microprocessor 8085?

The 8085 microprocessor is an 8-bit general-purpose processor developed by Intel in 1977. It became extremely popular in India because of its simple design, instruction set, and availability of kits in engineering labs.

Definition (Easy to remember):

A microprocessor 8085 is a programmable digital IC that fetches, decodes, and executes instructions to perform tasks like arithmetic, logic, controlling hardware, and data handling.

Designed by:

Intel engineer Federico Faggin

Used in:

– Calculators
– Early computers
– Embedded controllers
– Measurement systems
– Teaching labs (the most common use today)

History of Microprocessor 8085

The history of microprocessor 8085 starts with Intel’s earlier processors:

• 4004 → First commercial microprocessor
• 8080 → Widely used
• 8085 → Improved version of 8080 with fewer external components
• 8086 → Actual father of modern x86 architecture

Features of Microprocessor 8085

The most important features of microprocessor 8085 include:

• 8-bit processor: handles 8-bit data at a time
• 16-bit address bus: can address 64 KB memory
• 5 interrupts: TRAP, RST7.5, RST6.5, RST5.5, INTR
• Machine cycle: 8 control signals
• Clock frequency: 3.072 MHz
• Single +5V supply
• 74 instructions and 246 opcodes

Microprocessor 8085 Architecture

This is the heart of the Microprocessor 8085 complete guide.

When we talk about the architecture of microprocessor 8085, we discuss how all internal blocks work together—like ALU, registers, buses, and timing circuits.

Important Blocks in the 8085

• ALU – Performs arithmetic + logic
• Registers – Temporary data storage
• Accumulator – Most important register
• Instruction Register + Decoder
• Control Unit – Controls everything
• Interrupt Control
• Serial I/O Control
• Timing and Control Unit
• Address Buffer and Data Buffer

Block Diagram of Microprocessor 8085

Let’s explain the block diagram of microprocessor 8085 in the simplest way.

What the block diagram includes:

• ALU
• Register array (B, C, D, E, H, L, A)
• Program Counter
• Stack Pointer
• Temporary registers
• Interrupts
• Internal data bus
• Timing and control circuits

Why this matters?

Every exam question like “draw the architecture of microprocessor 8085” or “functional block diagram of microprocessor 8085” is based on this.

Pin Diagram of Microprocessor 8085

The pin configuration of microprocessor 8085 has 40 pins, and understanding these pins is mandatory for interfacing.

Important pins include:

• A0–A15 → 16 address pins
• AD0–AD7 → Multiplexed (Address/Data)
• ALE → Address Latch Enable
• RD, WR → Read/Write
• IO/M → Selects memory or I/O
• READY, HOLD, HLDA → DMA control
• TRAP, RST7.5, RST6.5, RST5.5, INTR → Interrupts

Instruction Set of 8085

Learning the microprocessor 8085 instruction set is the biggest part of programming. The instruction set includes:

• Data Transfer Instructions (MOV, MVI, LDA)
• Arithmetic Instructions (ADD, ADI, SUB)
• Logical Instructions (ANA, ORA, CMA)
• Branching Instructions (JMP, JC, JNZ)
• Stack Instructions (PUSH, POP)
• I/O Instructions (IN, OUT)

Working of Microprocessor 8085

If someone asks How does 8085 microprocessor work?, the simplest answer is:

1. Fetch the instruction
2. Decode the instruction
3. Execute the instruction

These are called Machine cycles, and each machine cycle has T-states.

Memory in Microprocessor 8085

8085 uses a 16-bit address bus, so:

Total memory it can address:

2ⁱ⁶ = 65536 bytes = 64 KB

Types of memory used:

• ROM → Stores programs
• RAM → Temporary data
• Stack memory → LIFO storage

Registers of Microprocessor 8085

8085 contains:

General Purpose Registers (GPRs):

B, C
D, E
H, L

Special registers:

• Accumulator
• Program Counter
• Stack Pointer
• Temporary registers
• Instruction register
• Flag register

Flag Register in Microprocessor 8085

The flag register (also called the status register) is an 8-bit register that shows the outcome of ALU operations.
Whenever the 8085 performs addition, subtraction, compare, or logic operation—these flags automatically update.

The 5 Flags Are:

1. S – Sign Flag
2. Z – Zero Flag
3. AC – Auxiliary Carry Flag
4. P – Parity Flag
5. CY – Carry Flag

Why flags matter?

Every conditional instruction (JC, JNC, JZ, JNZ, JP, JM) depends on these flags.
Without flags, the microprocessor cannot make decisions.

Interrupts in Microprocessor 8085

Interrupts allow the microprocessor to stop the current work and respond to an urgent request.

Types of Interrupts

8085 has five hardware interrupts:

Key Terms:

• INTR full form → Interrupt Request
• INTR’s sequence → Acknowledged through INTA’ signal
• Interrupt vector table → Stores service routines

Timing, Control and Machine Cycles

To understand how instructions execute, you must know the machine cycle of microprocessor 8085.

What is a Machine Cycle?

A set of T-states required to complete one operation like memory read, memory write, instruction fetch, etc.

Common Machine Cycles:

• Opcode Fetch Cycle
• Memory Read Cycle
• Memory Write Cycle
• I/O Read Cycle
• I/O Write Cycle
• Interrupt Acknowledge Cycle

Example:
Opcode Fetch = 4 T-states
Memory Read = 3 T-states

Addressing Modes of Microprocessor 8085

Addressing modes tell the processor where to find data.

8085 Has 5 Addressing Modes:

1. Immediate Addressing
2. Register Addressing
3. Direct Addressing
4. Indirect Addressing
5. Implied (Implicit) Addressing

Example:

• MVI A, 32H → Immediate
• MOV A, B → Register
• LDA 2050H → Direct
• MOV A, M → Indirect

Instruction Format of Microprocessor 8085

Every instruction in 8085 follows one of the following formats:

Three instruction formats:

• 1-byte instruction
• 2-byte instruction
• 3-byte instruction

Examples

• 1-byte → MOV A,B
• 2-byte → MVI A,32H
• 3-byte → STA 5000H

Assembly Language Programming in Microprocessor 8085

If you want to become confident in 8085, this part is important.

Simple 8085 Programs

1) Program to Add Two Numbers

MVI A, 25H
MVI B, 30H
ADD B
HLT

2) Program for Subtraction

MVI A, 90H
MVI B, 40H
SUB B
HLT

3) Program for Multiplication (Loop Method)

8085 has no MUL instruction, so we add in a loop.

Stack and Subroutines

Stack Pointer in 8085

• A 16-bit register
• Follows LIFO
• Important for PUSH, POP, CALL, RET instructions

Subroutine

A small block of code used repeatedly.

Example:

CALL 2000H
...
RET

Memory Interfacing in Microprocessor 8085

To connect RAM/ROM to the microprocessor, you must understand:

Key Signals Used in Memory Interfacing:

• RD’ → Read
• WR’ → Write
• IO/M’ → Select I/O or Memory
• ALE → Latch lower address

Memory Mapping Steps:

1. Decide memory size
2. Assign address range
3. Connect address lines
4. Connect control signals
5. Test with instructions

I/O Interfacing in Microprocessor 8085

The microprocessor communicates with external devices using:

Two types of I/O addressing:

1. Isolated I/O (IN, OUT instructions)
2. Memory-mapped I/O

Common Interfacing ICs Used:

• 8255 PPI
• 8253 Timer
• 8279 Keyboard/Display
• 8251 USART

Difference Between 8085 and 8086

Here is the simplest interview-style comparison:

Applications of Microprocessor 8085

The application of microprocessor 8085 includes:

• Traffic light control
• Washing machines (old models)
• Measurement systems
• Stepper motor control
• Data acquisition
• Simple embedded projects
• Educational use

Advantages and Disadvantages of Microprocessor 8085

Advantages

• Simple architecture
• Easy to program
• Requires only +5V
• Beginner-friendly
• Cost-effective

Disadvantages

• Limited memory (64KB)
• No multiplication/division instruction
• Slow compared to modern processors
• No pipeline

8085 Flag Register

The Flag Register in 8085 is an 8-bit special purpose register that indicates the status of the ALU operation. Out of 8 bits, five are active flags and the remaining are unused.

Active Flags

Understanding with Example

Instruction: MVI A, 0xFF then ADI 0x01

• Result = 00
• Z flag = 1
• CY flag = 1
• P flag = 1
• S flag = 0

This is classic interview question material!

8085 Timing Diagrams

What is a Timing Diagram?

It’s a visual representation of how control signals change during instruction execution.

Why Important?

8085 is used heavily in interviews because timing diagrams show:

• T-states
• Machine cycles
• Instruction cycles
• Memory Read/Write behavior

Example : Opcode Fetch Cycle

Example : Memory Read Timing

• T1: Address from PC is put on bus
• T2: RD = 0
• T3: Data from memory placed on data bus

These diagrams show hardware-level understanding very useful in embedded interviews.

Interrupt System of 8085 (Full Breakdown)

8085 has 5 hardware interrupts:

TRAP

• Cannot be disabled
• Edge + level triggered
• Used in emergency situations

RST 7.5

• Highest priority maskable interrupt
• Edge-triggered
• Must be acknowledged

RST 6.5 & 5.5

• Level-triggered
• Medium priority

INTR

• Completely programmable
• Requires INTA cycle for vector

This table is gold for interviews.

Interrupt Enable/Disable Instructions

Example:

EI     ; enable interrupts
MVI A, 0x20
SIM    ; mask RST 5.5

Serial Communication in 8085 (SID & SOD)

8085 has simple 1-bit serial I/O pins:

SID : Serial Input Data

Reads one bit at a time.

SOD : Serial Output Data

Writes one bit at a time.

Used with SIM/RIM.

Example:

MVI A, 01H  
SIM    ; send 1 bit through SOD

Though old, this concept is foundational for UART learning.

Addressing Modes (Expert Level)

8085 supports five addressing modes:

Why important?

Interviewers ask to convert C code to 8085 assembly → you must choose correct addressing mode.

8085 Instruction Set

Data Transfer Instructions

MOV, MVI, LXI, LDA, STA, LDAX, STAX

Arithmetic Instructions

ADD, ADI, SUB, INR, DCR, INX, DCX

Logical Instructions

ANA, ORA, XRA, CMA, RLC, RRC

Branch Instructions

JMP, JZ, JNZ, JC, JNC, CALL, RET

Machine Control

HLT, EI, DI, NOP, SIM, RIM

Each group serves different use cases — an easy way to remember.

8085 Memory Organization

8085 can address:

• 64 KB of memory total
• Separate I/O address space (256 bytes)

Memory Map Example:

Useful for designing embedded boards.

8085 Assembly Language Programs (With Explanation)

Program 1 : Add Two Numbers

MVI A, 25H
MVI B, 30H
ADD B
STA 3000H
HLT

Output: 55H stored at 3000H.

Program 2 : Find Largest Number in Array

LXI H, 2050H
MOV C, M
INX H
DCR C
MOV A, M
LOOP: INX H
CMP M
JNC NEXT
MOV A, M
NEXT: DCR C
JNZ LOOP
STA 3000H
HLT

Program 3 : BCD to Binary Conversion

Used in industrial control applications.

MVI A, 45H
ANI 0FH
MOV B, A
MVI A, 45H
ANI F0H
RRC
RRC
RRC
RRC
MVI C, 0AH
MUL: DCR C
JNZ MUL
ADD B
HLT

8085-Based System Design (Practical Guide)

Components you can interface:

• RAM (6264)
• ROM (2764)
• 8255 (Parallel Port)
• 8279 (Keyboard/Display Controller)
• 8251 (USART)
• 8253 (Timer)

Steps in System Design

1. Decide memory map
2. Connect address/data bus
3. Use 74LS373 latch for lower address
4. Connect ALE → latch
5. Use RD, WR, IO/M for decoding
6. Use address decoder (74LS138)
7. Interface peripherals

This is real embedded hardware knowledge.

Microprocessor 8085 Interview Questions

BEGINNER LEVEL 8085 INTERVIEW QUESTIONS

1. What is a microprocessor?
2. What is the 8085 microprocessor?
3. Why is it called 8085?
4. How many pins are available in 8085?
5. What is the clock frequency of 8085?
6. How many address lines does 8085 have?
7. How many data lines are in 8085?
8. What is the size of the data bus of 8085?
9. Name all general-purpose registers in 8085.
10. What is the accumulator in 8085?
11. What is the Program Counter (PC)?
12. What is the Stack Pointer (SP)?
13. What is the Flag Register in 8085?
14. Name all the flags in 8085.
15. What is the purpose of ALE (Address Latch Enable)?
16. What is the READY pin used for?
17. What is the HOLD signal used for?
18. What are SID and SOD pins?
19. What is the function of IO/M̅?
20. What is the purpose of the RESET IN pin?

INTERMEDIATE LEVEL 8085 INTERVIEW QUESTIONS

21. Draw and explain the architecture of 8085.
22. What is a multiplexed address/data bus?
23. Why are AD0–AD7 multiplexed in 8085?
24. What is a machine cycle?
25. What is a T-state?
26. Explain the opcode fetch cycle.
27. List all interrupt pins in 8085.
28. Which interrupt has the highest priority?
29. Which interrupt is non-maskable?
30. What is the difference between INTR and INTA?
31. What is SIM instruction?
32. What is RIM instruction?
33. What are the different addressing modes in 8085?
34. What is the function of HL pair?
35. What are the types of instructions in 8085?
36. What is the difference between CALL and RET?
37. What is the difference between JMP and JNZ?
38. What is the role of SP during PUSH and POP?
39. What is the purpose of the stack?
40. How many types of instruction lengths are in 8085?
41. What is the purpose of X1 and X2 pins?
42. What is meant by vector address?
43. What is the difference between IO-mapped and memory-mapped I/O?
44. What is the difference between MOV M, A and MOV A, M?
45. What is the function of RST instructions?
46. What are software interrupts?
47. What is the difference between EI and DI?
48. What is the purpose of the HOLD and HLDA signals?
49. Explain the READY signal in interfacing.
50. What are wait states?

ADVANCED LEVEL 8085 INTERVIEW QUESTIONS

51. What is the full interrupt priority structure of 8085?
52. What is TRAP and how does it work?
53. What is the difference between edge-triggered and level-triggered interrupts?
54. Explain instruction pipelining in 8085.
55. What are vectored interrupts?
56. What is bus contention?
57. What is bus idle state?
58. Explain the timing diagram of memory read cycle.
59. Explain the timing diagram of memory write cycle.
60. Explain the timing diagram of I/O read cycle.
61. Explain the timing diagram of I/O write cycle.
62. What is the purpose of the control signals RD̅ and WR̅?
63. What is the difference between STC and CMC?
64. What is the role of the ALU in 8085?
65. What is the function of the internal clock generator?
66. Explain the function of RESET OUT.
67. What is the serial communication capability of 8085?
68. How is the stack implemented in 8085?
69. What is the difference between RAL and RAR?
70. What is the difference between CMA and CMC?
71. Explain the flags affected during arithmetic instructions.
72. How does a conditional jump work internally?
73. What is meant by branching delay?
74. What is the function of DAD instruction?
75. What is program memory and data memory in 8085 context?

EXPERT LEVEL 8085 INTERVIEW QUESTIONS

76. How does 8085 support interrupt masking?
77. How does RST 7.5 differ from RST 6.5 and RST 5.5?
78. How is memory mapped in 8085?
79. How does 8085 communicate with peripheral chips?
80. Explain the hardware required to interface RAM with 8085.
81. How does 8085 store 16-bit data using an 8-bit bus?
82. Explain 8085 bus cycles in detail.
83. What is memory segmentation in 8085?
84. Describe the operation of the HOLD signal in DMA.
85. How is data transferred using DMA with 8085?
86. Describe the internal data flow of 8085 during an addition operation.
87. Explain how subroutine nesting works in 8085.
88. What are the advantages of vectored interrupts over polling?
89. How does 8085 differentiate between memory and I/O operations?
90. Explain the purpose of interrupt vector table.
91. How does 8085 fetch 3-byte instructions?
92. What is the use of PSW (Program Status Word)?
93. What is an instruction cycle and how is it composed?
94. Explain the difference between logical, arithmetic, and branching instructions.
95. What is the purpose of the accumulator during logical operations?
96. How does a carry propagate in multi-byte addition?
97. What is the role of temporary registers inside 8085?
98. Explain the concept of stack overflow and underflow in 8085.
99. How is memory decoding done for 8085?
100. Explain the complete 8085 reset sequence.

8085 Coding/Programming Interview Questions

BEGINNER-LEVEL 8085 CODING QUESTIONS

1. Write an 8085 program to add two 8-bit numbers.
2. Write an 8085 program to subtract two 8-bit numbers.
3. Write an 8085 program to add two 16-bit numbers.
4. Write an 8085 program to find 1’s complement of a number.
5. Write an 8085 program to find 2’s complement of a number.
6. Write an 8085 program to move data from one memory location to another.
7. Write an 8085 program to exchange the contents of H-L pair and D-E pair.
8. Write a program to increment a number stored in memory.
9. Write a program to decrement a number stored in memory.
10. Write an 8085 program to clear the accumulator.
11. Write a program to load immediate data into registers.
12. Write an 8085 program to implement a delay loop.
13. Write an 8085 program to copy a block of data from one location to another.
14. Write an 8085 program to compare two numbers.
15. Write a program to check if a number is positive or negative.
16. Write a program to mask upper nibble of accumulator.
17. Write a program to mask lower nibble of accumulator.
18. Write an 8085 program to rotate accumulator left (RAL).
19. Write an 8085 program to rotate accumulator right (RAR).
20. Write a program to swap nibbles of accumulator.

INTERMEDIATE-LEVEL 8085 CODING QUESTIONS

21. Write a program to find the largest number in an array.
22. Write a program to find the smallest number in an array.
23. Write a program to sort an array in ascending order.
24. Write a program to sort an array in descending order.
25. Write a program to count the number of positive numbers in an array.
26. Write a program to count the number of negative numbers in an array.
27. Write a program to reverse an array.
28. Write a program to search for an element in an array (linear search).
29. Write a program to calculate the sum of N numbers.
30. Write a program to calculate the average of N numbers.
31. Write an 8085 program to generate Fibonacci series.
32. Write an 8085 program to check whether a number is even or odd.
33. Write a program to multiply two 8-bit numbers (using repeated addition).
34. Write a program to divide two 8-bit numbers (repeated subtraction).
35. Write a program to convert BCD to binary.
36. Write a program to convert binary to BCD.
37. Write a program for binary to ASCII conversion.
38. Write a program for ASCII to binary conversion.
39. Write an 8085 program to find square of a number (lookup table).
40. Write a program to implement left shift operation.
41. Write a program to implement right shift operation.
42. Write an 8085 program to count number of 1s in a binary number (bit count).
43. Write a program to check palindrome number.
44. Write a program to check if two numbers are equal.
45. Write a program to transfer block of N bytes.

ADVANCED-LEVEL 8085 CODING QUESTIONS

46. Write an 8085 program to multiply two 16-bit numbers.
47. Write an 8085 program to divide a 16-bit number by an 8-bit number.
48. Write an 8085 program to perform 16-bit subtraction with borrow.
49. Write an 8085 program to perform 16-bit addition with carry.
50. Write a program to find factorial of a number.
51. Write an 8085 program to check for prime number.
52. Write an 8085 program to generate prime numbers within a range.
53. Write a program to find GCD of two numbers.
54. Write a program to find LCM of two numbers.
55. Write a program to generate delay of 1 second using loops.
56. Write a program to generate square wave using SOD line.
57. Write a program for keyboard interfacing using RIM/SIM.
58. Write an 8085 program to interface 7-segment display.
59. Write a program to display 0–9 continuously on 7-segment.
60. Write a program to interface 8255 PPI with 8085.
61. Write a program to read a byte from port A and output it to port B.
62. Write a program to control LEDs connected to 8255.
63. Write a program to scan a matrix keypad using 8255.
64. Write a program to read analog value through 8251 USART.
65. Write a program to generate waveform on DAC using 8085.
66. Write a program to perform block transfer using DMA.
67. Write a program to store data at consecutive memory locations until 00H is found.
68. Write an 8085 program to implement binary search.
69. Write an 8085 program to convert 2-digit hex to decimal.
70. Write a program to test specific bits of a number.

EXPERT-LEVEL 8085 CODING QUESTIONS

71. Write an 8085 program to perform floating-point addition.
72. Write an 8085 program to perform floating-point multiplication.
73. Write a program to implement software delay with precise calculation.
74. Write a program to simulate stack operations using memory.
75. Write a program to implement queue data structure in 8085.
76. Write a program to implement stack data structure in 8085.
77. Write an 8085 program to evaluate an arithmetic expression.
78. Write an 8085 program to implement CRC calculation.
79. Write an 8085 program to compute checksum of a data block.
80. Write a program to encrypt data using XOR key.
81. Write a program to decrypt XOR-encrypted data.
82. Write a program to calculate 16-bit checksum (Internet checksum style).
83. Write an 8085 routine to handle TRAP interrupt.
84. Write a program to create custom software interrupt using RST instruction.
85. Write a program to interface ADC0808 with 8085.
86. Write a program to read temperature sensor data using ADC.
87. Write a program for real-time clock simulation.
88. Write an 8085 program to implement PWM using delay loops.
89. Write a program to detect key debounce in keyboard input.
90. Write an 8085 bootloader (memory copy from ROM to RAM).
91. Write a program for bubble sort on 16-bit numbers.
92. Write a program for insertion sort on 16-bit numbers.
93. Write a program for quick sort using recursion (stack-based).
94. Write a program to simulate UART transmission.
95. Write a program to simulate UART reception.
96. Write a program to generate a ramp waveform using DAC.
97. Write a program to generate a sine wave using lookup table.
98. Write a program to compute square root of a number.
99. Write a recursive program for Fibonacci series.
100. Write an 8085 interrupt-driven data acquisition program.

Microprocessor 8085 FAQ

When it comes to mastering ESP microcontrollers, developers often struggle to find a single place where everything—from basics to advanced real-world projects—is explained clearly.
That’s why resources like Embedded Prep Master have become extremely valuable for students, embedded engineers, and hobbyists.

One of the best guides available today is:

Complete ESP Tutorials (Beginner to Advanced) : ESP32 Tutorials

This guide is a complete gateway for anyone who wants to learn ESP32, ESP8266, IoT development, sensor interfacing, Wi-Fi programming, and real embedded-system projects.

Raj Kumar

Mr. Raj Kumar is a highly experienced Technical Content Engineer with 7 years of dedicated expertise in the intricate field of embedded systems. At Embedded Prep, Raj is at the forefront of creating and curating high-quality technical content designed to educate and empower aspiring and seasoned professionals in the embedded domain.

Throughout his career, Raj has honed a unique skill set that bridges the gap between deep technical understanding and effective communication. His work encompasses a wide range of educational materials, including in-depth tutorials, practical guides, course modules, and insightful articles focused on embedded hardware and software solutions. He possesses a strong grasp of embedded architectures, microcontrollers, real-time operating systems (RTOS), firmware development, and various communication protocols relevant to the embedded industry.

Raj is adept at collaborating closely with subject matter experts, engineers, and instructional designers to ensure the accuracy, completeness, and pedagogical effectiveness of the content. His meticulous attention to detail and commitment to clarity are instrumental in transforming complex embedded concepts into easily digestible and engaging learning experiences. At Embedded Prep, he plays a crucial role in building a robust knowledge base that helps learners master the complexities of embedded technologies.

embeddedprep.com/