---
title: "Microprocessor vs microcontroller; 8051 addressing"
subject: "Embedded System"
chapter: 9
key: "semester_6/embedded_system:8051-addressing-modes-micro-vs-processor"
source: https://www.bctengineer.com/q/semester_6/embedded_system/8051-addressing-modes-micro-vs-processor
site: BCT Engineering
---

# Microprocessor vs microcontroller; 8051 addressing

Embedded System · Chapter 9: Microcontrollers in Embedded Systems

- Asked in: 2064 Poush (old course)
- Video: [Difference between Microprocessor and Microcontroller](https://www.youtube.com/watch?v=dcNk0urQsQM) — ALL ABOUT ELECTRONICS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/embedded_system/8051-addressing-modes-micro-vs-processor
- Whole chapter: https://www.bctengineer.com/md/semester_6/embedded_system/chapter-9

## Question

Differentiate Microprocessor and Microcontroller highlighting its uses. Also explain the Addressing Modes of 8051 microcontroller.

## Answer

#### Microprocessor versus microcontroller

| Point | Microprocessor | Microcontroller |
|---|---|---|
| Chip contains | CPU only | CPU, RAM, ROM, I/O ports, timers, serial port |
| External chips | Needed for memory and I/O | Few or none |
| Size, cost, power | Larger, costlier, higher power | Smaller, cheaper, low power |
| Instructions | Rich, for data processing | Bit-oriented, for control |
| Speed | High (GHz) | Low (MHz) |
| Uses | PCs, laptops, servers, workstations | Embedded: washing machine, remote control, ATM, car ECU, toys |
| Examples | 8085, 8086, Core i7 | 8051, AVR, PIC, ARM Cortex-M |

#### Addressing modes of the 8051

The addressing mode specifies where an instruction finds its operand.

| Mode | Operand is | Example | Meaning |
|---|---|---|---|
| Immediate | a constant in the instruction, marked with # | MOV A,#25H | A = 25H |
| Register | in R0-R7 of the active bank (or A, B) | MOV A,R3 | A = R3 |
| Direct | at an 8-bit internal RAM or SFR address | MOV A,30H | A = RAM[30H] |
| Register indirect | at the RAM address held in R0 or R1 | MOV A,@R0 | A = RAM[R0] |
| Indexed | in code memory at base + offset | MOVC A,@A+DPTR | A = ROM[DPTR + A] |

1. **Immediate:** the data is in the instruction: `MOV R2,#10`, `MOV DPTR,#4000H`.
2. **Register:** the operand is in a register: `ADD A,R5`. Short and fast.
3. **Direct:** the instruction holds the 8-bit address: `MOV 40H,#5`, `MOV A,P1`. It is the only way to access SFRs.
4. **Register indirect:** R0 or R1 is a pointer: `MOV A,@R1`; with `INC R1` it scans an array. External RAM: `MOVX A,@DPTR`.
5. **Indexed:** for look-up tables in ROM: `MOVC A,@A+DPTR`, `MOVC A,@A+PC`, `JMP @A+DPTR`.
6. **Bit addressing:** single bits are accessed with `SETB P1.0`, `CLR C`, `JB P2.1,LABEL`.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What mainly distinguishes a microcontroller chip from a microprocessor chip?
   A. It contains only the CPU
   B. It contains CPU plus RAM, ROM, I/O ports, timers and serial port
   C. It runs at GHz speeds with rich instructions
   D. It always needs external memory chips
   Answer: B. A microcontroller integrates memory, I/O and peripherals with the CPU, while a microprocessor contains the CPU only. (Key point: Chip contents)

2. Which application is best suited to a microcontroller such as the 8051?
   A. Personal computer
   B. Server
   C. Washing machine controller
   D. Workstation
   Answer: C. Microcontrollers are used in embedded control products like washing machines, remotes and ATMs; PCs and servers use microprocessors. (Key point: Typical uses)

3. In MOV A,30H on the 8051, how is the operand found?
   A. 30H is a constant loaded into A
   B. It is in register R3
   C. It is read from internal RAM address 30H
   D. It is read from code memory at 30H
   Answer: C. Direct addressing gives the 8-bit address of internal RAM or SFR in the instruction, so A = RAM[30H]. (Key point: Direct addressing)

4. Which 8051 addressing mode is used for look-up tables in ROM, as in MOVC A,@A+DPTR?
   A. Immediate
   B. Register indirect
   C. Direct
   D. Indexed
   Answer: D. Indexed addressing reads code memory at base (DPTR or PC) plus offset A, ideal for look-up tables. (Key point: Indexed addressing)

## Related in Embedded System

- [Microcontroller vs microprocessor; 8051 features](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Amicro-vs-microprocessor-8051-features) — Embedded System, chapter 9, asked 2×
- [Addressing modes of 8051](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3A8051-addressing-modes) — Embedded System, chapter 9, asked 4×

## Related in other subjects

- [Microprocessor vs microcontroller](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Amicroprocessor-vs-microcontroller) — Microprocessor, chapter 1
- [Instruction and data format, addressing modes](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3A8085-instruction-data-format-addressing) — Microprocessor, chapter 2, asked 2×
- [Addressing modes of 8086](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3A8086-addressing-modes) — Microprocessor, chapter 3, asked 2×
- [Features and addressing modes of 8085](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3A8085-features-addressing-modes) — Microprocessor, chapter 2