8051 vs 8085 : Understand the key differences

The 8051 is developed by Intel in 1980. It is an 8-bit microcontroller designed for embedded applications. It belongs to the MCS-51 family of microcontrollers and has been widely adopted due to its versatility and ease of use.

The 8085 is introduced by Intel in 1976. It is an 8-bit microprocessor used primarily for educational purposes and simple control applications. It belongs to the 8-bit microprocessor family and is known for its simplicity and ease of understanding.

Features of 8051 Microcontroller

8051 is the microcontroller developed by Intel. Following are the features of 8051 Microcontroller:
• It houses 8 bit CPU.
• 4 KByte ROM used for code or program storage
• 128 Byte RAM to store data or variables used in program
• 32 Input/Output lines with 4 ports ( 8 lines per port)
• 2 Timers used for introducing delay and for setting the baud rate for data communication.
• 1 serial Port with one TxD and one RxD line used for serial communication with external devices.
• 6 Interrupt Sources
• Clock oscillator circuit runs at 12MHz frequency.

The figure-1 depicts 8051 microcontroller architecture. Refer 8051 Architecture➤

Microcontroller Architecture Intel 8051 core

Features of 8085 Microprocessor

8085 is the microprocessor developed by Intel. Following are the features of 8085 Microprocessor:
• It is 8 bit size processor developed as single chip using N-MOS.
• It has multiplexed address and data bus on 8 lines AD0 to AD7.
• The maximum clock frequency used in 8085 is 3 MHz.
• It has 40 pins and runs at 5V power supply.
• There are 5 hardware interrupts viz. TRAP, INTR, RST5.5, RST6.5, RST7.5
• It has about 74 programming instructions with 4 addressing modes.
• It does not house memory, but it has 16 address lines which can access 64K bytes (2^16) of externally connected memory.
• It has 8 bit lines which can address 256 (~2^8) ports connected externally.
• It has two serial lines viz. SID and SOD. These can be connected with serial peripherals.
• It consists of ACC, one flag register, 6 general purpose registers and two special registers(SP-Stack Pointer, PC-Program Counter).

The figure-2 depicts 8085 architecture. Refer 8085 Architecture➤

8085 microprocessor architecture

Difference between 8051 and 8085

Following table summarizes similarities and difference between 8051 and 8085.


Specifications 8051 8085
Architecture Harvard architecture Von Neumann architecture
Data Bus Width 8-bit 8-bit
Address Bus Width 16-bit 16-bit
Program Memory Internal ROM ( Up to 4 KB) External ROM
RAM Internal RAM (128 bytes) External RAM
Clock Speed Up to 24 MHz 3 MHz to 6 MHz
Instruction set Complex (Includes bit, byte and block operations) Simple
Timers/Counters 2 or more (depending on the variant) None (requires external peripherals)
I/O Ports 4 ports (32 I/O lines) None (requires external peripherals)
Serial Communication Built-in UART None (requires external peripherals)
Interrupts 5 interrupt sources 5 interrupt sources
Power Consumption Low power consumption Relatively higher power consumption
DMA Access signals NO YES, Has HOLD and HLDA signals
Peripheral Interfaces Built-in support for I2C, SPI, and more Requires external interfacing ICs
Development Ease Easier with more integrated peripherals More complex, requires additional components
Applications Embedded systems, automotive, consumer electronics Basic computing, control systems
Programming 8051 programming➤ 8085 programming➤

Conclusion : The 8051 microcontroller and the 8085 microcontroller serve different purposes and are designed with different architectures. The 8051 is more suited for modern embedded systems with its integrated peripherals and ease of development, while the 8085 is typically used in educational settings and simpler control applications. Understanding their differences is key to choosing the right microcontroller for a specific application.

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