Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

difference between at89c51 & at89s51

Not open for further replies.


Newbie level 5
Jun 15, 2005
Reaction score
Trophy points
Activity points
difference between at89c51 and at89s51

Could any body tell me abot the difference betwin 89c51 & 89s51

in the data sheet i got the pins status are the same but the flash memory of both mcu is in system programmable but the 89s51 only have pins allocated for in system programming. what about 89c51 in systemm programming?

difference between 8051 and 89c51


I think studying the datasheets of both versions would make it more clear to you. as far as i know that 89s51 can be directly programmed by serial port and 89c51 cannot be.


difference between 89c51 and 89s51

A simple presence of flash memory alterable when the 8951 is supplied only with +5v was strong enough for a good advertisement.
A voltage of +12v was not so common available in the electronic boards based on microcontroller supplied at +5v.
Thus, such a kind of microcontrollers with internal flash memory program, alterable only at +12v, have to be removed from the board and programmed in external programmers.
When Atmel's AT89C51 was released with internal flash memory alterable at +5v, Atmel claimed that can be in user-system reprogramable (no external programmer required).
This has been specially mentioned in the datasheet as a good advertisement for the product they developed. Watch out to "user" and "re"
However, even if the +12v was not required for reprogram in the user-system (the high voltage programming is still possible in external programmer) the AT89C51 still needs a lot of I/O pins to be reprogrammed.

Thus the Atmel felt the need of a new microcontroller based on 8051 core that must provide a true ISP (In System Programming) with only few I/O pins involved in programming.
AT89S51 released few years later, can be programmed in the system through SPI interface which requires only 4 pins.

As I explained in a previous thread, the AT89S51 inherits most of the features provided by AT89C51 since both are based on 8051 core.
Including almost the same layout for datasheet.
Thus, you can't see any big difference between statements like:

In System Reprogrammable for AT89C51 (watch the "re" in the first page of datasheet which confused yarajit)


In System Programmable (ISP) for AT89S51 (watch the missing "re" in the datasheet)

Like I said it's only a matter of english and Atmel advertisement.

Hope that my english knowledges helped me to explain these difference between AT89C51 and AT89S51.
Not open for further replies.

Part and Inventory Search

Welcome to