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Discussion Groups | Comp.Arch.Embedded | What is a Hex buffer?

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What is a Hex buffer? - Baxter - 2006-06-22 20:35:00

I've got a circuit that has a Hex Buffer (specifically, a TI SN74LVC07A).

I'm trying to determine what this chip does - what its function is. I
reviewed the datasheet, but it doesn't tell me anything - at least not in a
way I can understand.

(yes, I'm a newbie at this stuff.)

-- 
---------------------------------------------------------------------
DataGet® & PocketLog®  www.dataget.com
Data Collectors               www.baxcode.com
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Re: What is a Hex buffer? - Steve at fivetrees - 2006-06-22 21:20:00

"Baxter" <l...@baxcode.com> wrote in message 
news:1...@corp.supernews.com...
> I've got a circuit that has a Hex Buffer (specifically, a TI SN74LVC07A).
>
> I'm trying to determine what this chip does - what its function is. I
> reviewed the datasheet, but it doesn't tell me anything - at least not in 
> a
> way I can understand.
>
> (yes, I'm a newbie at this stuff.)

"Hex" in this case just means there's 6 of 'em. (Not hexadecimal, which 
would be 16, just hex - no decimal.)

Ok - the 7407 generic part is a 6-way open-drain buffer.(Available in 
various logic families since the 70s.) This means that there are 6 buffers, 
each with a logic family-compatible input, and each with an output which is 
capable of sinking some (depending on family) current, and no inversion 
(i.e. a HIGH input means high output, i.e. no sink, and a LOW input means a 
low output, i.e. the output is sinking current).

Does that help?

Steve
http://www.fivetrees.com 



Re: What is a Hex buffer? - Baxter - 2006-06-22 22:56:00

"Steve at fivetrees" <s...@NOSPAMTAfivetrees.com> wrote in message
news:7...@pipex.net...
> "Baxter" <l...@baxcode.com> wrote in message
> news:1...@corp.supernews.com...
> > I've got a circuit that has a Hex Buffer (specifically, a TI
SN74LVC07A).
> >
> > I'm trying to determine what this chip does - what its function is. I
> > reviewed the datasheet, but it doesn't tell me anything - at least not
in
> > a
> > way I can understand.
> >
> > (yes, I'm a newbie at this stuff.)
>
> "Hex" in this case just means there's 6 of 'em. (Not hexadecimal, which
> would be 16, just hex - no decimal.)

Interesting.  I came across some sites where they were comparing Hex buffers
agains Octal buffers.  So resolving one issue raises another - but seems
tangental to what I'm after.

>
> Ok - the 7407 generic part is a 6-way open-drain buffer.(Available in
> various logic families since the 70s.) This means that there are 6
buffers,

good.

> each with a logic family-compatible input, and each with an output which
is
> capable of sinking some (depending on family) current, and no inversion
> (i.e. a HIGH input means high output, i.e. no sink, and a LOW input means
a
> low output, i.e. the output is sinking current).
>
Here you lose me - I don't know what 'sinking some current' means (in
practical terms).

I understand it does NOT invert the signal (make high voltage low, and low
voltage high).  Do you mean that it keeps the current constant as the
voltage fluctuates?



Re: What is a Hex buffer? - Mike Warren - 2006-06-22 23:13:00

Baxter wrote:
> Interesting.  I came across some sites where they were comparing Hex
> buffers agains Octal buffers.  So resolving one issue raises another
> - but seems tangental to what I'm after.

Octal buffers have 8 in one package.

>> each with a logic family-compatible input, and each with an output
>> which is capable of sinking some (depending on family) current, and
>> no inversion (i.e. a HIGH input means high output, i.e. no sink, and
>> a LOW input means a low output, i.e. the output is sinking current).
>>
> Here you lose me - I don't know what 'sinking some current' means (in
> practical terms).

It means able to pull a high level signal low. The standard terms are
"source current" which means it outputs a high level and "sink current"
which means it outputs a low level. In the case of the ICs under
discussion, they have an open drain (or collector) which means to
see a high level on the pin it needs to be pulled high by a resistor.

-Mike



Re: What is a Hex buffer? - CBFalconer - 2006-06-22 23:25:00

Baxter wrote:
> "Steve at fivetrees" <s...@NOSPAMTAfivetrees.com> wrote in message
>
... snip ...
> 
>> each with a logic family-compatible input, and each with an output
>> which is capable of sinking some (depending on family) current, and
>> no inversion (i.e. a HIGH input means high output, i.e. no sink, and
>> a LOW input means a low output, i.e. the output is sinking current).
>
> Here you lose me - I don't know what 'sinking some current' means (in
> practical terms).
> 
> I understand it does NOT invert the signal (make high voltage low, and
> low voltage high).  Do you mean that it keeps the current constant as
> the voltage fluctuates?

No, think of it as a switch between the output pin and the ground
pin.  When the input is low that switch is closed, so the output is
at ground potential (with a restriction on the maximum current
drawn).  When the input is high the switch is open, and the output
circuit goes wherever the external circuitry takes it.

The usual external circuitry is simply a resistor to Vcc.  That
means various open collector buffers can be connected to that node,
and any one of them can drive the point low.  This is known as a
wired or (for negative logic).

The difference between open-collector and the more usual output
circuit is that the normal circuit will actively drive the output
node high.  It can't be used in the wired or configuration, but the
logic swings take place faster for rising output edges.  Outputs
can't be directly connected together because they could fight, with
often fatal results.

-- 
Chuck F (c...@yahoo.com) (c...@maineline.net)
   Available for consulting/temporary embedded and systems.
   <http://cbfalconer.home.att.net> USE maineline address!



Re: What is a Hex buffer? - Grant Edwards - 2006-06-22 23:26:00

On 2006-06-23, Baxter <l...@baxcode.com> wrote:

>> "Hex" in this case just means there's 6 of 'em. (Not hexadecimal, which
>> would be 16, just hex - no decimal.)
>
> Interesting.  I came across some sites where they were comparing Hex buffers
> agains Octal buffers.  So resolving one issue raises another

Raises what issue?  You do know that the prefix "oct" means
eight, right?

-- 
Grant Edwards                   grante             Yow!  Now I'm telling MISS
                                  at               PIGGY about MONEY MARKET
                               visi.com            FUNDS!

Re: What is a Hex buffer? - 2006-06-23 01:23:00

Baxter, 

Does every message comes with your SPAM?


Re: What is a Hex buffer? - Baxter - 2006-06-23 01:41:00

"Grant Edwards" <g...@visi.com> wrote in message
news:1...@corp.supernews.com...
> On 2006-06-23, Baxter <l...@baxcode.com> wrote:
>
> >> "Hex" in this case just means there's 6 of 'em. (Not hexadecimal, which
> >> would be 16, just hex - no decimal.)
> >
> > Interesting.  I came across some sites where they were comparing Hex
buffers
> > agains Octal buffers.  So resolving one issue raises another
>
> Raises what issue?  You do know that the prefix "oct" means
> eight, right?
>
I'm primarily a software guy - Octal means base 8 number - Hex is 16-bit
number.



Re: What is a Hex buffer? - Baxter - 2006-06-23 01:50:00

"Mike Warren" <m...@or-this-csas.net.au> wrote in message
news:449b5c6e$0$490$6...@uq-127creek-reader-03.brisbane.pipenetworks.com.au...
> Baxter wrote:

> >> each with a logic family-compatible input, and each with an output
> >> which is capable of sinking some (depending on family) current, and
> >> no inversion (i.e. a HIGH input means high output, i.e. no sink, and
> >> a LOW input means a low output, i.e. the output is sinking current).
> >>
> > Here you lose me - I don't know what 'sinking some current' means (in
> > practical terms).
>
> It means able to pull a high level signal low. The standard terms are
> "source current" which means it outputs a high level and "sink current"
> which means it outputs a low level. In the case of the ICs under
> discussion, they have an open drain (or collector) which means to
> see a high level on the pin it needs to be pulled high by a resistor.
>
Still pretty murky to me.  The Hex Buffer connects to various pins on a
MSP430.  Inside the MSP430, I'm setting the pin (voltage) high or low - I
just can't quite picture how the Hex Buffer affects that.  As far as that
goes, I'm still wrestling a bit with the semantics of a "pull-up" resistor.



Re: What is a Hex buffer? - Alan - 2006-06-23 02:23:00

On Thu, 22 Jun 2006 22:50:51 -0700, "Baxter"
<l...@baxcode.com> wrote:

>"Mike Warren" <m...@or-this-csas.net.au> wrote in message
>news:449b5c6e$0$490$6...@uq-127creek-reader-03.brisbane.pipenetworks.com.au...
>> Baxter wrote:
>
>> >> each with a logic family-compatible input, and each with an output
>> >> which is capable of sinking some (depending on family) current, and
>> >> no inversion (i.e. a HIGH input means high output, i.e. no sink, and
>> >> a LOW input means a low output, i.e. the output is sinking current).
>> >>
>> > Here you lose me - I don't know what 'sinking some current' means (in
>> > practical terms).
>>
>> It means able to pull a high level signal low. The standard terms are
>> "source current" which means it outputs a high level and "sink current"
>> which means it outputs a low level. In the case of the ICs under
>> discussion, they have an open drain (or collector) which means to
>> see a high level on the pin it needs to be pulled high by a resistor.
>>
>Still pretty murky to me.  The Hex Buffer connects to various pins on a
>MSP430.  Inside the MSP430, I'm setting the pin (voltage) high or low - I
>just can't quite picture how the Hex Buffer affects that.  As far as that
>goes, I'm still wrestling a bit with the semantics of a "pull-up" resistor.
>

A buffer is a device used to increase the drive capability of another
chip.  The output of an IC can drive a certain number of inputs on
other chips (depends on IC family, etc.).  If you don't have enough
drive output to drive all the inputs you need then buffers are used to
increase the output drive (think of them as amplifiers).

Buffers can either be non-inverting or inverting depending on what you
need to do. Obviously non-inverting buffers give you a high output for
a high input and a low output for a low input.  Inverting buffers
operate the opposite way around (low out for high in ,etc.).

Buffers also come in different package configurations the common ones
being hex (=6) or octal (=8).

Buffers can also be open collector/drain outputs or active driven
outputs.  Open collector outputs normally need external pull-up
resistors or circuitry (so called because the resistor pulls up the
un-driven open collector output of the buffer towards the positive
supply voltage).

HTH
Alan

--
Sell your surplus electronic components at 
http://ozcomponents.com
Search or browse for that IC, capacitor,
crystal or other component you need.

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