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'[EE]: Totem Pole Outputs in 74HC164'
2001\10\02@092057 by jeethur

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Hi,
       I've got a small little doubt about the outputs of
       74HC164. Are the outputs of these ICs totem pole ?
       In other words, Does the IC pull down the output to
       ground when one of its outputs is low ?

       I have designed a moving message display with a 74HC238
       Multiplexer and a few 74HC164s. But out here, 238s are
       not available. So, I have to use 74HC138 which is the
       same as 238 but with inverted outputs. If the 164 can pull
       its output pin low (like a PIC), this problem could be solved
       with a small change in the PIC software.

Thanks,

Jeethu Rao

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2001\10\03@061143 by Vasile Surducan

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On Tue, 2 Oct 2001, Jeethu Rao wrote:

> Hi,
>         I've got a small little doubt about the outputs of
>         74HC164. Are the outputs of these ICs totem pole ?
>         In other words, Does the IC pull down the output to
>         ground when one of its outputs is low ?


Rao, any ttl output which is not open colector is totem-pole. LS164 have
IOL = 8mA and IOH = - 0.4mA.
Vasile

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2001\10\03@121105 by raphael

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This is my first ever reply!

I believe yes. I don't know if it's "totem pole" in particular.

one way to be sure is to set up a circuit to make the pin slowly change states, and hook up led's from that pin to ground and from that pin to vdd (observing polarity).  if they both light when they should, you have what you want.

I am not to be trusted: check the datasheet!

-raphael



>Date:    Tue, 2 Oct 2001 18:49:11 +0530
>From:    Jeethu Rao <jeethurspamKILLspamSANCHARNET.IN>
>Subject: [EE]: Totem Pole Outputs in 74HC164
>
>Hi,
>       I've got a small little doubt about the outputs of
>      74HC164. Are the outputs of these ICs totem pole ?
>     In other words, Does the IC pull down the output to
>    ground when one of its outputs is low ?

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2001\10\04@053304 by Bob Barr

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Jeethu Rao wrote:
{Quote hidden}

Yep, the Philips datasheet "HCMOS Family Characteristics" lists all of the
DC specs. It has specs for V sub OH and V sub OL at a few different current
values ranging up to several mA.

Regards, Bob

>
> > {Original Message removed}

2001\10\04@071645 by dr. Imre Bartfai

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Hi,

I did not understand the question at all. An output may be either
totem-pole or open-collector. Even if it is not totem-pole (i. e. open
collector) it is definitely capable to pull down the connected pin (the
common mistake when using RA4 in PIC).

Regards,
Imre



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On Thu, 4 Oct 2001, Bob Barr wrote:

{Quote hidden}

> > > {Original Message removed}

2001\10\04@074111 by Vasile Surducan

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Imre, I think he have problems with load, mostly parasitical LED lighting
whithout any command.
A totem-pole output may have (if it's a correct design) greatest loads to
ground ( small resistors ) or smallest loads (large resistors) connected
to VCC accordingly to IOL and IOH specifications. If the load does not
meet with this, the output will be out of TTL requirements and the output
voltage levels may have unexpected values.
It's the situation with not only a microcontroller input is connected to a
TTL output.
But you knew that, I'm sure.
Cheers,
Vasile

On Thu, 4 Oct 2001, dr. Imre Bartfai wrote:

{Quote hidden}

> > > > {Original Message removed}

2001\10\05@043726 by jeethur

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Thanks guys for your repiles.
I could'nt find anything in the Philips DataSheet
which mentions Totem Pole. But I saw a design in
Elektor which mentions 164 has totem pole outputs.
And The design is a construction project(hence tried and tested)

So, I believe totem pole it is.

Jeethu Rao

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2001\10\05@095007 by Bob Barr

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Jeethu Rao wrote:
>
>Thanks guys for your repiles.
>I could'nt find anything in the Philips DataSheet
>which mentions Totem Pole. But I saw a design in
>Elektor which mentions 164 has totem pole outputs.
>And The design is a construction project(hence tried and tested)
>
>So, I believe totem pole it is.
>

Don't believe it; know it. The fact that Philips doesn't use the words
"totem pole" is totally irrelevent.

TTL/HCMOS outputs can only be either 1) totem pole or 2)
open-collector/open-drain respectively. If it ain't one, it's the other.

If the part has a V sub OH spec at x current, *something* is pulling the
output high (i.e. the top half of the totem pole).

Regards, Bob


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2001\10\05@145314 by uter van ooijen & floortje hanneman

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> TTL/HCMOS outputs can only be either 1) totem pole or 2)
> open-collector/open-drain respectively. If it ain't one, it's the other.

Actually totem-pole with tri-state capability could (should?) be counted as
a third kind of output.

Wouter van Ooijen
Van Ooijen Technische Informatica: http://www.voti.nl
Jal compiler for PIC uC's:  http://www.xs4all.nl/~wf/wouter/pic/jal

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2001\10\05@153443 by Bob Barr

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wouter van ooijen & floortje hanneman wrote:
>
> > TTL/HCMOS outputs can only be either 1) totem pole or 2)
> > open-collector/open-drain respectively. If it ain't one, it's the other.
>
>Actually totem-pole with tri-state capability could (should?) be counted as
>a third kind of output.
>

True, my oversight. I probably should have included that one as well.

Electrically, though, when a tri-state pin is in its output mode, the pin
acts like any other totem-pole output. That's probably why I tend to think
of tri-states as just totem-poles with an on-off switch. :=)

Regards, Bob


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2001\10\06@023308 by jeethur

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Yeps, you're right. And now the problem has been fixed.

Jeethu Rao

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2001\10\07@003236 by jeethur

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> Don't believe it; know it. The fact that Philips doesn't use the words
> "totem pole" is totally irrelevent.

I downloaded the Philips HC User Guide. It mentions Totem Pole.
BTW, even Microchip does'nt call it Totem Pole. They call it Tristate.

> TTL/HCMOS outputs can only be either 1) totem pole or 2)
> open-collector/open-drain respectively. If it ain't one, it's the other.

Verified Ok. It works!

Thanks,

Jeethu Rao

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2001\10\08@065345 by Vasile Surducan

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On Fri, 5 Oct 2001, wouter van ooijen & floortje hanneman wrote:

> > TTL/HCMOS outputs can only be either 1) totem pole or 2)
> > open-collector/open-drain respectively. If it ain't one, it's the other.
>
 ...if we split the wire in four then 2) is open-x because CMOS can be
open drain or either open source... and from here to tristate open-x is
only one little step.

regards, Vasile

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