The main difference between them lies in the following points:
Pin function: Pins almost identical changes were, in the AT89S51 in P1.5, P1.6, P1.7 have a second function, that is, the second 3-pin serial ISP function formed programming interface.
Programmability: AT89C51 only supports parallel programming, But AT89S51 supports both parallel programming and ISP programming.
Voltage in the programming area, AT89C51 in addition to normal programming voltage of 5V, another 12v is needed for Vpp. But AT89S51 just need to be 4-5V.
Endurance: AT89C51 flash memory can be programmed upto 1000 times while the AT89S51 can be programmed from 1000-10000 times, so that the learner repeated the beginning of a more favorable programmer, reducing learning costs.
Frequency: AT89C51 limits the operating frequency is 24MHZ, and AT89S51 maximum operating frequency is 33MHZ, (AT89S51 chip in two models, to support the maximum operating frequency of 24MHZ and 33MHZ) in order to have a faster computing speed.
Power Supply: AT89S51 operating voltage range is up to 4-5.5V, while the AT89C51 at the end of the 4.8V and 5.3V.
Anti-jamming more: AT89S51 has integrated watchdog timer (Watchdog Timer), and AT89C51 needs an external watchdog timer circuit, or single-chip software constitute the internal watchdog timer to achieve anti-jamming software.
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