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'Off the top of your head, USART question...'
2000\02\22@163157 by Erik Reikes

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Does anyone know, off the top of their head, if I set the TRIS register to
1 (receive) for my USART TX line if it will actually go into Hi-Z input mode?

I'm wondering if I also need to clear the SPEN bit as well.

I need to do this for power savings...  I'm going to try it out ASAP, but I
thought someone just might know.

Thanks.


Erik Reikes
Software Engineer
Xsilogy, Inc.

spam_OUTereikesTakeThisOuTspamxsilogy.com
ph : (858) 535-5113
fax : (858) 535-5163
cell : (858) 663-1206

2000\02\22@170920 by paulb

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Erik Reikes wrote:

> Does anyone know, off the top of their head, if I set the TRIS
> register to 1 (receive) for my USART TX line if it will actually go
> into Hi-Z input mode?

 My interpretation of the goss on this is that you *must* set the TRIS
bit to 1 anyway for the transmitter to operate.

> I'm wondering if I also need to clear the SPEN bit as well.

 You would, it seems, need to do this to disable the UART TX line.

> I need to do this for power savings...

 TX output won't consume current unless you connect a load to it.  What
load is connected?
--
 Cheers,
       Paul B.

2000\02\22@173001 by Tony Nixon

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"Paul B. Webster VK2BZC" wrote:
>
> Erik Reikes wrote:
>
> > Does anyone know, off the top of their head, if I set the TRIS
> > register to 1 (receive) for my USART TX line if it will actually go
> > into Hi-Z input mode?
>
>   My interpretation of the goss on this is that you *must* set the TRIS
> bit to 1 anyway for the transmitter to operate.

I've always set the TRIS bit to 0 on the TX line, and never had any
problems.

I don't think it matters when the SPEN bit is enabled as it seems to
override the TRIS settings.


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Best regards

Tony

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2000\02\22@195247 by Kelly J Kohls

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On Tue, 22 Feb 2000 13:35:35 -0800 Erik Reikes <ereikesspamKILLspamXSILOGY.COM>
writes:
> Does anyone know, off the top of their head, if I set the TRIS register
to 1 (receive) for my
> USART TX line if it will actually go into Hi-Z input mode?
>
> I'm wondering if I also need to clear the SPEN bit as well.

I'm not sure of the TRIS or SPEN bits, but I know that if you clear the
TXEN bit, the UART output will go into a high impedance state.  Hope this
helps.


Kelly Kohls, N5TLE
Dallas, TX
Email:  .....kkohlsKILLspamspam.....juno.com  OR  EraseMEn5tlespam_OUTspamTakeThisOuTqsl.net  OR n5tlespamspam_OUTarrl.net
Homepage:  http://www.qsl.net/n5tle/

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2000\02\22@205204 by Erik Reikes

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At 06:43 PM 2/22/00 -0600, you wrote:
>On Tue, 22 Feb 2000 13:35:35 -0800 Erik Reikes <@spam@ereikesKILLspamspamXSILOGY.COM>
>writes:
>> Does anyone know, off the top of their head, if I set the TRIS register
>to 1 (receive) for my
>> USART TX line if it will actually go into Hi-Z input mode?
>>
>> I'm wondering if I also need to clear the SPEN bit as well.
>
>I'm not sure of the TRIS or SPEN bits, but I know that if you clear the
>TXEN bit, the UART output will go into a high impedance state.  Hope this
>helps.
>

I'll try this out and get back to the list, but in looking at the Block
diagram for the TX pin, it looks to me like the TXEN only enables the SPBRG
to go through to the TSR register.  I'm looking on page 110 of DS30292A the
16f87x reference manual.

I also was unable to find any reference to TXEN tri-stating the output.

I think I must set the appropriate TRISC bit, and clear SPEN, thereby
reverting back to a normal input pin.

Thanks for the suggestion, definitely worth looking at.


Erik Reikes
Software Engineer
Xsilogy, Inc.

KILLspamereikesKILLspamspamxsilogy.com
ph : (858) 535-5113
fax : (858) 535-5163
cell : (858) 663-1206

2000\02\23@232705 by Kelly J Kohls

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> I'll try this out and get back to the list, but in looking at the Block
diagram for the TX pin, it
> looks to me like the TXEN only enables the SPBRG to go through to the
TSR register.  I'm
> looking on page 110 of  DS30292A the 16f87x reference manual.
>
> I also was unable to find any reference to TXEN tri-stating the output.

I probably should have mentioned this in my earlier post........

It's not in the 16F876 datasheet.   I found the information in the 16C76
datasheet (document # DS30390E, page 106, last sentence of the paragraph
below the grey box).  For some reason, this information was omitted when
they compiled the 16F876 datasheet.  I have a project that originally
used the 16C76 and took advantage of this "feature".  When I made the
transition to the 16F876 everything ran just fine.  I hope this
information helps as well.


Kelly Kohls, N5TLE
Dallas, TX
Email:  RemoveMEkkohlsTakeThisOuTspamjuno.com  OR  spamBeGonen5tlespamBeGonespamqsl.net  OR TakeThisOuTn5tleEraseMEspamspam_OUTarrl.net
Homepage:  http://www.qsl.net/n5tle/

________________________________________________________________
YOU'RE PAYING TOO MUCH FOR THE INTERNET!
Juno now offers FREE Internet Access!
Try it today - there's no risk!  For your FREE software, visit:
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