Details about 89C51

Thread Starter


Joined Jun 13, 2007
I am a newbie here and about the programming of the 89C51 microcontroller.I have downloaded the data sheet avaliable on the .But i really want to know more about the memory the internal hardware of the 89C51, i am unable to find anything in the stickies also .Please suggest a link to the above detail's ,i do have a book on 8051 programming so i am really interested in the hardware details like
"bi-directional open drain " things in the data sheet .
thank you in advance


Joined Feb 24, 2006
You want the following two documents from the atmel website:

Microcontroller Instruction Set

8051 Hardware Manual

The second document describes the hardware present in each of the 8051 variants. The datasheets for the individual parts document the additional features of the part.

The key feature of the quasi-bi-directional port structure is that writing a one to an output port with a VERY WEAK pullup is equivalent to making that pin an input. The pin can only source 60 micro amps so any reasonable output driver can pull it low without damaging anything.

The open drain structure on P0 means you have to provide an external pullup resistor for those pins which are to be outputs.

After drinking from the firehose, feel free to ask more questions.