The difference between AT89c51 and AT89S51 microcontrollers

      AT89S51 is a low-power, high-performance CMOS 8-bit single-chip microcomputer. It contains 8k Bytes ISP (In-system programmable) Flash read-only program memory that can be repeatedly erased and written 1000 times. The device is manufactured using ATMEL's high-density, non-volatile storage technology, compatible with the standard MCS-51 instruction system and 80C51 pin structure. The chip integrates a general 8-bit central processor and ISP Flash storage unit. The powerful microcomputer AT89S51 can provide cost-effective solutions for many embedded control application systems.
      AT89S51 has the following features: 40 pins, 8k Bytes Flash on-chip program memory, 128 bytes of random access data memory (RAM), 32 external bidirectional input/output (I/O) ports, 5 interrupt priority levels, 2 levels of interrupt nesting, 2 16-bit programmable timer counters, 2 full-duplex serial communication ports, watchdog (WDT) circuit, and on-chip clock oscillator.
     In addition, the AT89S52 is designed and configured with an oscillation frequency of 0Hz and a power saving mode that can be set by software. In idle mode, the CPU suspends work, while the RAM timer counter, serial port, and external interrupt system can continue to work. The power-down mode freezes the oscillator and saves the RAM data, stopping other chip functions until the external interrupt is activated or the hardware is reset. At the same time, the chip also has three packaging forms, including PDIP, TQFP, and PLCC, to meet the needs of different products.
      Compared with AT89C51, AT89S51 has exactly the same appearance pins. The HEX program of AT89C51 can be directly run on AT89S51 without any conversion, and the results are the same. AT89S has some new functions compared to AT89C51, and supporting online programming and watchdog are the main features.           
        The main differences between them are as follows:
       1. Pin function: The pins are almost the same, and the changes are that in AT89S51, P1.5, P1.6, and P1.7 have a second function, that is, the second function of these three pins constitutes the interface for serial ISP programming.
       2. Programming function: AT89C51 only supports parallel programming, while AT89S51 not only supports parallel programming but also supports ISP online programming. In terms of programming voltage, in addition to the normal working 5V, the programming voltage of AT89C51 requires 12V Vpp, while AT89S51 only requires 4-5V.
       3. Higher number of programming times: The nominal number of programming times of AT89S51 is 1000 times, but it is actually 1000-10000 times, which is more conducive to repeated programming for beginners and reduces the learning cost.
       4. Higher operating frequency: The maximum operating frequency of AT89C51 is 24MHZ, while the maximum operating frequency of AT89S51 is 33MHZ, (AT89S51 chip has two models, supporting the maximum operating frequency of 24MHZ and 33MHZ respectively), thus having a faster computing speed. 
       5. Wider power supply range: AT89S51 has an operating voltage range of 4-5.5V, while AT89C51 cannot work properly when the voltage is lower than 4.8V or higher than 5.3V. 
       6. Stronger anti-interference ability: AT89S51 has an internal integrated watchdog timer, while AT89C51 needs an external watchdog timer circuit, or uses the internal timer of the microcontroller to form a software watchdog to achieve software anti-interference.