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AT89s52 Port 0 always HIGH

chetan_129

Jan 26, 2020
2
Joined
Jan 26, 2020
Messages
2
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
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,700
Joined
Nov 17, 2011
Messages
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Probably unrelated to your problem, but: PSEN is an output and should not be tied to VCC.
 
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