Rest problem 89C2051

Discussion in '8bit Microcontrollers' started by ClueLess, Feb 23, 2008.

  1. ClueLess

    ClueLess Guest

    Hi all

    I am just toying with 89C2051 and I have assembled a program to switch
    on a series of LEDs using the rl a instruction. The program works well
    on the simulator. But I cannot make it work on the breadboard.

    The problem is with the reset. I am using an available 32.768kHz
    crystal, I have used the standard 33pf caps too.

    On the reset pin I have tried 1 uf, 10uf capacitors and also
    resistances of various values to the ground from the reset pin. Still
    no go.

    Can someone in the know among you help me with some leads?

    Thanks for your time and attention

    ClueLess
     
    ClueLess, Feb 23, 2008
    #1
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  2. ClueLess

    Eeyore Guest

    Why do you think the problem is with the reset ?

    It's only 2 components. You can hardly go wrong ! How have you connected
    it ?

    Graham
     
    Eeyore, Feb 23, 2008
    #2
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  3. ClueLess

    Eeyore Guest

    I'd check that the watch crystal is designed to be used with 33pF caps.
    The first one I looked at is designed for use with 12pF caps.

    Graham
     
    Eeyore, Feb 23, 2008
    #3
  4. ClueLess

    ClueLess Guest


    Since I did not have a 12pf cap handy I tried with a 4 mHz crystal
    with 33pf caps. Still no go. As I said the code works very well in the
    simulator.

    Any more suggestions?

    Thanks for taking time to help me

    ClueLess
     
    ClueLess, Feb 24, 2008
    #4
  5. ClueLess

    ClueLess Guest


    Since I did not have a 12pf cap handy I tried with a 4 mHz crystal
    with 33pf caps. Still no go. As I said the code works very well in the
    simulator.

    Any more suggestions?

    Thanks for taking time to help me

    ClueLess

    PS: Did not see this after several hours. So posting again :-(
     
    ClueLess, Feb 25, 2008
    #5
  6. ClueLess

    ClueLess Guest

    Well, it started working when I caught hold of the crystal with my
    fingers :-(

    True, it seems to want more capacitor. But it is totally not in
    agreement with what I have read.

    How this can be?

    ClueLess
     
    ClueLess, Feb 26, 2008
    #6
  7. ClueLess

    Eeyore Guest

    You mean it's OK now ? Good to hear.

    I expected it to want less capacitance actually !

    Do you have the manufacturer's data for that specific crystal you are using
    ? If not, you need to get it.

    Beware of things like stray capacitance from PCB traces and also it may be a
    good idea to ground the cystal's metal can.

    Graham
     
    Eeyore, Feb 26, 2008
    #7
  8. ClueLess

    ClueLess Guest

    The data sheet says 12.5 pf which I do not have at the moment,
    unfortunately. I will have to order it.

    Meantime I modified the program to work with a 4 mHz crystal and 33 pf
    caps and it worked first shot.

    So it is only the crystal interfacing - the key is in the caps, I
    think.

    I will post the results once I get hold of the 12.5 pf stuff.

    Thanks for your continued interest in helping me


    ClueLess
     
    ClueLess, Feb 28, 2008
    #8
  9. ClueLess

    ClueLess Guest


    Hi Graham

    I got a clue from someone in the 8052.com to insert a 300k resistor
    between the crystal and the xtal2 pin. And it worked.

    Problem solved. And again thanks for your interest.

    ClueLess
     
    ClueLess, Feb 28, 2008
    #9
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