Many beginners 51 single-chip users will have such a question: What is AT89S51? Books and web tutorials are all 8051, 89C51, etc. I have not heard of 89S51?!
Here, beginners should clarify a product concept in the practical use of single-chip microcomputers. The MCS-51 single-chip microcomputer is a product launched by INTE in the United States in 1980. The typical product has 8031 ​​(there is no internal program memory, and the actual use has been eliminated by the market), 8051 (The chip adopts HMOS, the power consumption is 630mW, which is 5 times of 89C51, the actual use has been eliminated by the market) and the general products such as 8751. Until now, the MCS-51 core series compatible MCU is still the mainstream product of the application (such as Currently popular 89S51, 89C51 has been discontinued, etc.), the training materials of colleges and universities and professional schools are still based on the theoretical basis of MCS-51 microcontroller.
Some documents even refer to the MCS-51 series of single-chip microcomputers. The 8051 is the most typical representative of the early days. Due to the far-reaching influence of the MCS-51 microcontroller, many companies have introduced compatible series of single-chip microcomputers, which means that the MCS-51 core has actually Become a standard for 8-bit microcontrollers.
Other companies' 51 MCU products are compatible with the MCS-51 core. The same piece of program, the results run on the hardware of each microcontroller manufacturer are the same, such as ATMEL 89C51 (has been discontinued), 89S51, PHILIPS (Philips), and WINBOND (Huabang), etc., we often say The discontinued 89C51 refers to ATMEL's AT89C51 single-chip microcomputer. At the same time, it has enhanced many features, such as clocks. It is better to use Flash (the program memory can be rewritten at least 1000 times). The memory is taken with the original ROM. (Write once), the performance of the AT89C51 is already very good compared to the 8051.
However, in terms of marketization, the 89C51 has been challenged by the PIC microcontroller camp. The most fatal flaw of the 89C51 is that it does not support the ISP (Online Update Program) function. It must add new features such as the ISP function to better extend the legend of the MCS-51. 89S51 is to replace 89C51 in this background. Now, 89S51 has become a new darling in the practical application market. Atmel, which is the market share first, has discontinued AT89C51 and will replace it with AT89S51. The 89S51 has been improved in terms of technology. The 89S51 uses a new 0.35 process, which reduces costs and increases functionality and competitiveness. The 89SXX can be compatible with 51 series chips such as 89CXX. At the same time, Atmel no longer accepts orders from 89CXX. The 89C51 that everyone sees on the market is actually a huge inventory of Atmel's pre-production. If the market needs it, Atmel can of course resume production of the AT89C51.
New features added to the 89S51 over the 89C51 include:
-- A lot of new features, performance has been greatly improved, the price is basically the same, even lower than the 89C51!
-- ISP online programming function, the advantage of this function is that the program in the MCU memory does not need to be stripped from the working environment. It is a powerful and easy to use feature.
-- The highest operating frequency is 33MHz. Everyone knows that the 89C51's limit operating frequency is 24M, which means that S51 has a higher operating frequency and thus has a faster calculation speed.
-- Has a duplex UART serial channel.
-- Internally integrated watchdog timer, no need to external watchdog timer unit circuit like 89C51.
-- Double data indicator.
-- Power off indicator.
-- A new encryption algorithm, which makes the decryption of the 89S51 impossible, and the confidentiality of the program is greatly enhanced, so that the intellectual property can be effectively protected from being infringed.
-- Compatibility: Fully compatible with 51 full-word series products. For example, 8051, 89C51 and other early MCS-51 compatible products. In other words, all textbooks, web tutorials (whether the one used in the textbook is 8051 or 89C51 or MCS-51, etc.) can be run as usual on the 89S51. This is called backward compatibility. 
Ningbo Autrends International Trade Co.,Ltd. , https://www.supermosvape.com