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AT89s52 Port 0 always HIGH

Discussion in 'Microcontrollers, Programming and IoT' started by chetan_129, Jan 26, 2020.

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  1. chetan_129

    chetan_129

    2
    0
    Jan 26, 2020
    Hi,
    I have made an AT89S52 board on zero pcb ( the schematic is shown in the attachment)and burned the below code in controller.
    The problem is PORT 0 is always HIGH(0XFF). all the other ports are showing expected result(0XAA). I have tried keeping Pin PSEN both HIGH and LOW but nothing worked.
    I have also checked resister pack connections and the resistance between port pins and VCC. it is also correct.
    PORT 2 has the same kind of res pack and same connections and its working fine, so what could be wrong with PORT 0?
    Any kind of help is appreciated.
    Thanks!!!
    Code:
    org 0
    mov a,#0xaa
    mov P0,a
    mov P1,a
    mov P2,a
    mov P3,a
    
    sjmp $
    89s52.png 89s52.png
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,544
    1,970
    Nov 17, 2011
    Probably unrelated to your problem, but: PSEN is an output and should not be tied to VCC.
     
  3. chetan_129

    chetan_129

    2
    0
    Jan 26, 2020
    Is there any possibility that only PORT 0 is damaged and not the remaining ports ??? if yes, how can i check it.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    9,544
    1,970
    Nov 17, 2011
    Try another chip.
     
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