atmel uc at89c51ed2 port problems

[dk]

hi
i have been using atmel AT89C51ED2 microcontroller . the problem i am facing
is that i can make toggle port 0 pins (open drain outputs, with external pull ups,
but i have beev not able to toggle or rather make other port pins low specifiaclly
those ports that have internal pull ups.
1) i have disabled the internal pull up thru software
2) i gave the ports pins external pull ups but still i cant lower the port pins ,
as per datasheet this port pins with internal pull ups are quasi bidirectional ports
the ports pins toggles mometarily , it can send data bursts but but doesnt go to low state even if the software commands it do so.
Can any one help me

 

[mrcube_ns]

What value of pull ups are you using? Maybe you used to small resistant value?

It should be 10kOhm.


Mr.Cube

 

[dk]

hi
i have tried the combination of 10k ohm but it didnt work.i would like to know sir
whether the we can set any port pin low through software commands which are quasi bidirectional in nature .
If this is possible then how it can be done.
thanks and regards
dk

 

[mrcube_ns]

So if I understand well when you send command like PORT2=0 you still have +5V on some (or all) pins on this port.

Is this case try to change mcu, cause this is not normal behavior.

Mr.Cube

 

[nicleo]

For Port 1, 2, and 3, no pull up resistors are required. Try the following code:

      MOV A, #55H
BACK: MOV P1, A
      ACALL DELAY
      CPL A
      SJMP BACK

All the bits of P1 should toggle continuously.