Why are 8-bit 8051 MCUs still in use?



 

The venerable 8-bit 8051 microcontroller is still selling in high volumes. What gives?

 

Embedded systems are dynamic regarding efficiency and functionality as every often microcontroller units (MCUs) evolve and new versions are introduced in the market. Over the last four decades, embedded systems have evolved vigorously with the invention of some legendary 8-bit MCUs such as Intel MCS-51 also known as 8051 which is used in many products to date. But of course, there are limitations to 8-bit controllers, and they cannot beat 32-bit MCUs in many features. Then why are they still in use and are they going to last in trend for long?

Figure 1: Block diagram of the Intel® 8051 microcontroller, a series of MCUs first developed in 1980 with a CISC instruction set and Harvard architecture for embedded use. By Appaloosa – Own work, CC BY-SA 3.0.

8-bit 8051 MCUs are Still Running in Commercial Products

Even after almost 40 years after launching, the Atmel 89C51 (8051 based) MCU is still widely used for educational purposes. Nowadays, the Atmel 89C51 based project development boards are readily available in the market which means they are still in demand.[i] Apart from academics, the 8051 is widely used in wireless communication systems. Various companies are offering wireless products with an 8051 core. Although the 8051 is a bit old-fashioned, these wireless systems are equipped with modern functionality. The 8051 based wireless transceivers are still in use as they offer excellent performance with optimized power consumption. [ii] Some brands are selling Bluetooth HC-10 4.0 BLE Modem Modules build with an 8051 core. [iii] These modules are evidence of the 8051 MCU’s popularity in times when 32- and 64-bit processors rule technology. There are 8051 based Bluetooth gadgets that are also available online with helpful user reviews. [iv] Some Wireless Power Meters available in the market also use an 8051 8-bit core. These power meters primarily use 8051 in the wireless transmission system. [v]

Similarly, many other 8-bit MCUs are still in commercial use, and they are expected to retain their position in technology for a long time due to significant features at a cut-rate cost.

Power Consumption

Modern 32-bit MCUs are extensively powerful as compared to 8-bit MCUs regarding power management features. Although 32-bit MCUs effectively manage active mode, they can remain inactive when no instructions are being executed and can wake up shortly before any execution. The sleep/wake feature saves considerable power as well, which is not possible with traditional MCUs such as 8051.

However, for low power products that require simple periodic sensing, using a 32-bit MCU is comparatively uneconomical thus the 8051 is a more suitable choice. [vi]

Peripheral Features

The 8051 has 32 general-purpose input/output (GPIO) and two timers which are more than enough for development of low-scale embedded projects. However, there are various features that 8-bit MCUs such as the 8051 lack. For example, 8051 MCUs cannot read analog signals directly, and external circuits have to be connected for reading analog signals, whereas modern MCUs are capable of reading analog signals directly.

High-Frequency Clocking

The clock rate of an 8-bit MCU is typically around 8 MHz, while modern 32-bit MCUs have clocking speeds up to hundreds of MHz. [vii] A typical Cortex M7 microprocessor based STM32F7 series MCU operates at 216 MHz. [viii] Although modern MCUs offer unmatchable speed as compared to 8-bit MCUs, 8 MHz is a considerable speed for a variety of applications. Speed is a significant concern in applications that involve extensive code executions required over a short period. However, in applications where high frequency is essential but achieving very high frequency is not a priority, 8-bit MCUs can serve the purpose. [ix]

Limited Memory

Memory specifications also affect an MCU’s speed, as the Random Access Memory (RAM) offers memory for processing instructions. Most 8-bit MCUs like the 8051 have 128 KB of on-chip RAM, which is not even close to that of modern 32-bit MCUs. The limited 64 KB flash memory of the 8051 MCU creates barriers in the development of complex programs with large code, whereas modern 32-bit STM32F7 series MCUs offer up to 2 MB of flash memory. [x]

Economic Perspective

It’s true that 8-bit MCUs are cheap and suitable for devices like thermometers, digital counters, and wireless modules that do not require high-level features and have to be developed on a tight budget. However, 8051 MCUs are already obsolete for several technologies, such as the Internet of Things (IoT); mainly because they cannot handle a high level of network complexities.

Although 32-bit MCUs have more functions as compared to 8-bit MCUs, many vendors are more interested in developing cost-effective products, and that is what keeps 8-bit MCUs alive. Even today, Microchip sells more 8-bit MCUs than 32-bit MCUs and generates significant revenue.[xi] An Atmel 89C51 costs less than one dollar, whereas an Arm® Cortex™-M3 based STM32103 costs around three dollars.

Communication Protocols

All 8051 MCUs are prone to limited communication protocols. The 8051 doesn’t support communication protocols like Controller Area Network (CAN), Ethernet, Multiple Universal Asynchronous Receiver-transmitter (UART) and Universal Serial Bus (USB). For such applications 32-bit MCUs are more preferable, as they support multiple protocols efficiently. Various Space applications require multiple protocols at a time, therefore 32-bit controllers are widely used in space applications. The ESTCube-1 Satellite contains ST Microelectronics’ STM32F103, which is a 32-bit MCU. [xii]

Figure 2: The first Estonian satellite and first satellite in the world to attempt to use an electric solar wind sail (E-sail). It was launched on 7 May 2013. (Image Credit: Erik Kulu – University of Tartu, ESTCUBE team).

Temperature Range

MCUs are often exposed to extreme temperatures in some applications. The 8051 MCU can withstand −55 °C to +125 °C [xiii] which is almost the same as temperature range for 32-bit STM32F7 series MCUs. [xiv] So in a way, 8-bit MCUs are more reliable in extreme environments.

The venerable 8051 MCU has been in use for several decades and is still widely used in a panoply of products. It seems fairly clear that the 8-bit MCU has a niche that has not been disturbed over the years, primarily fixed in the same market space due to cost, size, simplicity, and its wide occupancy of established sockets.

 


Bilal Qamar is an Electrical Engineer. Nowadays he works as a technical writer and is studying Data Science. Bilal’s experience includes working on R&D projects at the Pakistan Space and Upper Atmosphere Research Commission, including design and development work on the Telemetry Transmitter and Telecommand Receiver for Pakistan National Student Satellite-1. Bilal has actively participated in engineering events and won multiple competitions across Pakistan. In college, he served as President of Electrical and Control Engineering Society at The University of Lahore.

 

 

[i] https://www.amazon.com/INSIGNIA-LABS-Development-P89V51RD2-SST89E516RD/dp/B07KDTY2MR/ref=sr_1_7?ie=UTF8&qid=1548797999&sr=8-7&keywords=8051+development+board

[ii] http://www.ti.com/product/CC2511

[iii] https://www.amazon.com/UNIVERSAL-SOLDER-SIMPLY-SMARTER-ELECTRONICS-2525/dp/B07GD74CTJ/ref=sr_1_29?ie=UTF8&qid=1548787641&sr=8-29&keywords=8051+core

[iv] https://www.alibaba.com/product-detail/High-performance-and-low-power-MCU_60391542233.html?spm=a2700.7724838.2017115.93.106b4e3dyptiH4

[v] https://www.alibaba.com/product-detail/Good-Quality-Integrated-Power-meter-with_60770229988.html?spm=a2700.galleryofferlist.normalList.129.60741e813LizGS

[vi] https://www.digikey.com/en/articles/techzone/2014/feb/is-there-a-future-for-8-bit-mcus

[vii] https://resources.altium.com/pcb-design-blog/8-bit-vs-32-bit-mcu-choosing-the-right-microcontroller-for-your-pcb-design

[viii] https://www.st.com/en/microcontrollers/stm32f7-series.html?querycriteria=productId=SS1858

[ix] https://resources.altium.com/pcb-design-blog/8-bit-vs-32-bit-mcu-choosing-the-right-microcontroller-for-your-pcb-design

[x] https://www.st.com/en/microcontrollers/stm32f7-series.html?querycriteria=productId=SS1858

[xi] http://deedoc.com/2018/03/17/8-bit-dead/

[xii] http://nuts.cubesat.no/upload/2016/03/12/hardware_review_magne_normann.pdf

[xiii] http://www.keil.com/dd/docs/datashts/atmel/at89c51_ds.pdf

[xiv] https://www.st.com/en/microcontrollers/stm32f7-series.html?querycriteria=productId=SS1858

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