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'power up state of 68hc11 ports'
1997\01\26@135120 by John van Zijl

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Hello world,

I am currently designing a board with a hc11 as a main processor. But i
don't know
what the state of the output lines are after power up. I hope that they are
low but I can't find anny info on the subject.

Thanks for the trouble.

John van Zijl from Holland.

1997\01\26@154804 by Philippe TECHER

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>what the state of the output lines are after power up. I hope that they are
>low but I can't find anny info on the subject.

What port are you talking about ?
All port are in high impedance input state at reset, this is the normal
situation after a reset, specially for a HC11. But it's also true for
many other microcontroller, because the chip designer doesn't know
what it is connected to.

Hope this will help you.
       Philippe.

1997\01\26@154804 by Philippe TECHER

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>what the state of the output lines are after power up. I hope that they are
>low but I can't find anny info on the subject.

What port are you talking about ?
All port are in high impedance input state at reset, this is the normal
situation after a reset, specially for a HC11. But it's also true for
many other microcontroller, because the chip designer doesn't know
what it is connected to.

Hope this will help you.
       Philippe.

1997\01\27@202802 by John Payson

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> >what the state of the output lines are after power up. I hope that they are
> >low but I can't find anny info on the subject.
>
> What port are you talking about ?
> All port are in high impedance input state at reset, this is the normal
> situation after a reset, specially for a HC11. But it's also true for
> many other microcontroller, because the chip designer doesn't know
> what it is connected to.

On chips whose pins are all programmable as inputs or outputs, it is customary
to have all pins set to inputs on reset.  There are, however, a few notable
exceptions:

[1] On the HC11 (your original query) I believe one of the I/O ports is output
   only and defaults to being high (significantly pulled) on reset.

[2] On the PICs, all pins are tri-stated, but on some PICs certain pins may
   default to analog inputs rather than digital ones; reading port A on the
   16C62x, for example, requires enabling the digital inputs.

   *CONFUSION ALERT* You do not have to enable the digital inputs on the
   16C62X port A in order to output stuff there, BUT any BSF/BCF, etc. on
   port A will clear any output whose corresponding input is not enabled.
   This can be *VERY CONFUSING* if you aren't expecting it.

[3] On the Intel 8x51 and related chips, all of the I/O's are either open-
   collector outputs or else open-collector outputs with weak pull-ups; they
   default to being high on reset (which is to say, for most of them, not
   quite tri-stated.  Note that this means 8x51 outputs cannot directly con-
   trol any type of power device safely since it's impossible to cover your
   bases both in the power-failed and power-up-reset states.

[4] One bizarre exception to the rule about 8x51 I/O's is the Philips 87C575.
   This one defaults to having all of its outputs pulled hard low on reset.
   Wierd.


'power up state of 68hc11 ports'
1997\02\01@232656 by Sarunas Cepulis
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John Payson wrote:
>
> > >what the state of the output lines are after power up. I hope that they are
> > >low but I can't find anny info on the subject.
> >
Hi,
all DDRx registers after RESET are cleared (to 0) & this
meaning that all ports are set to INPUT.Thats mean that
all ports are in HIGH IMPEDANCE condition.Log 0 or 1 hawe
no reason...
Just read PINK BOOKS.
Best regards,
       Saras.
P.S. on other processors, that i now , is same.

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