Many beginners who are new to 51 microcontrollers often ask: What is AT89S51? Why do books and online tutorials mention 8051, 89C51, but not 89S51?
It’s important for newcomers to understand the product concepts behind microcontroller usage. The MCS-51 series was introduced by Intel in 1980, with key models like 8031 (no internal program memory, now obsolete), 8051 (using HMOS technology, high power consumption, also obsolete), and 8751. Despite being outdated, the MCS-51 core remains a popular choice today. Modern variants like 89S51 and 89C51 (which has been phased out) are still widely used in education and industry. Most university textbooks and training programs are based on the MCS-51 architecture.
The term "MCS-51" refers to the entire family of 8-bit microcontrollers. The 8051 was the most famous early model, and due to its widespread influence, many companies developed compatible versions. This made the MCS-51 core a standard in the 8-bit microcontroller market.
Several manufacturers produced 51-series MCUs that were compatible with the MCS-51 core. For example, ATMEL's 89C51 (now discontinued), 89S51, Philips, and Winbond all created similar chips. While 89C51 was once common, it has since been replaced by more advanced models like 89S51. These newer versions offer enhanced features such as Flash memory, which allows rewriting up to 1,000 times, compared to the one-time programmable ROM of older models.
Despite these improvements, the 89C51 faced competition from PIC microcontrollers. One major drawback of 89C51 was the lack of ISP (In-System Programming) support, making updates difficult. To address this, Atmel introduced the 89S51, which improved upon the 89C51 in several ways, including a higher operating frequency (up to 33MHz), an integrated watchdog timer, and better security features.
Key features of the 89S51 over the 89C51 include:
- Enhanced performance with a higher operating frequency (33MHz vs. 24MHz)
- ISP functionality for easy programming without removing the chip
- Integrated watchdog timer
- Dual data pointer and power-down mode
- New encryption algorithm for better program protection
- Full backward compatibility with earlier 51-series chips
As a result, the 89S51 has become a preferred choice in many practical applications. It offers better performance, lower cost, and more advanced features than its predecessors. While 89C51 is still available in some markets, it is largely considered outdated. If you're looking for a reliable and modern 51-series microcontroller, the 89S51 is definitely worth considering.
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