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???
04/09/05 08:58
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 		 #91286 - Pull-ups
Responding to: ???'s previous message
Plz guide me....... urgent

If it is so urgent why not read datasheet? It is available at ATmel Website.

http://www.atmel.com/atmel/acrobat/doc0401.pdf

Does AT AT89S8252 require pullup resisteance

Again, the answer is in datasheet as follows:

Port 0 is an 8-bit open drain bi-didirectional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs.

Port 0 can also be configured to be the multiplexed low-order address/data bus during accesses to external program and data memory. In this mode, P0 has internal pull-ups.

Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pull-ups are required during program verification.


Now what purpose you are using port0 for? If it is for general purpose I/O, then you need pull up resistors on P0. 10K seems a reasonable value.

Is it a case of wroong pull up used

It seems a case of pull-ups used in wrong way, not wrong value.

  • Check if you have connected the common of pull-up array to +5V?

  • Also if you have used SIP/SIL resistor pack, have you noted a dot on the common pin? This pin (with dot) should be connected to +5V.

  • If there is anyother thing connected to port0, remove it and then check if you can get full 5V.


    • PS: Please avoid SMS in future.



    List of 6 messages in thread
    TopicAuthorDate
    at89s8252 PULL UP REQD?            01/01/70 00:00      
       Pull-ups            01/01/70 00:00      
          another thing            01/01/70 00:00      
             uh-oh            01/01/70 00:00      
       thanks            01/01/70 00:00      
          not 10k ??            01/01/70 00:00      

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