Subject:
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Re: Trouble working with PORTC
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 20 Jan 2001 23:25:01 GMT
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Viewed:
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3071 times
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Yes, I'm answering myself. I now notice that Port C is being used by the
LCD. Therefore, I'm guessing that this is part of the problem (the whole
problem, a really big problem?).
I'm still curious as to how Port C might be shared - is it still possible to
use it as an input port? What issues should I be concerned about for this?
What steps/considerations should I be aware of when thinking about sharing
Port C?
> I'm having a little trouble working with Port C on my 68hc11.
>
> A little background: the 68hc11 is part of a rug warrior pro. This board
> brings Port C out to an expansion socket which I can access. I'm generally
> using Interactive C 3.1 to work with the board.
>
> What I'd like to do is to use a pin, let's say PC0, to drive an LED. So,
> given what I've read in the 6811 Reference Manual, I should turn on bit 0 in
> the DDRC register. Unfortunately, I'm having trouble doing that and I don't
> quite know why.
>
> With the board attached, here are the results of some peeks, pokes and
> bit_clears:
>
> With nothing attached to Port C:
>
> peek(0x1003) = 3 (PORTC)
> peek(0x1007) = 7 (DDRC)
>
> Question 1: why is there any value on PORTC? Nothing is attached and the
> voltages are low - is it just transient or is there a reason bits 0 and 1
> are high, while bits 2 through 7 are low?
>
> Question 2: why is there any value on DDRC? The result of 7 suggests that
> bits 0, 1 and 2 are set for output. Why? My reading of the manual suggests
> this should be initialized to 0 (input) on reset.
>
> With a resistor between PC0 and ground (btw, if this is not a good thing to
> do, please tell me!):
>
> peek(0x1003) = 2
> peek(0x1007) = 6
>
> I can understand why PORTC went from 3 to 2. However, I can't understand why
> this would cause the DDRC register to change value. Can anyone explain that
> to me?
>
> Lastly, I can't seem to affect the state of the DDRC register through
> software. I would think that the following would change the value of DDRC:
>
> poke(0x1007, 0) /* turn off all DDRC bits */
>
> yet a peek(0x1007) immediately after returns a 7 (assume no resistor to
> ground on PC0).
>
> Likewise, the following has no effect on DDRC:
>
> bit_clear(0x1007, 0b00000001); /* turn off bit 0 */
>
> I feel like I'm missing something basic. Does anyone have any suggestions on
> what I'm doing wrong? Also, if it isn't too much trouble, suggestions on the
> steps necessary to drive an LED from PC0 would be great.
>
> Thanks again!
>
>
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Message is in Reply To:
 | | Trouble working with PORTC
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| I'm having a little trouble working with Port C on my 68hc11. A little background: the 68hc11 is part of a rug warrior pro. This board brings Port C out to an expansion socket which I can access. I'm generally using Interactive C 3.1 to work with (...) (26 years ago, 20-Jan-01, to lugnet.robotics.handyboard)
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