What is a Hex buffer?

Started by Baxter June 22, 2006
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.)

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"Baxter" <lbax02.spamguard@baxcode.com> wrote in message 
news:129mdrmtivdop5a@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
"Steve at fivetrees" <steve@NOSPAMTAfivetrees.com> wrote in message
news:7u6dnYXK1bVD3AbZnZ2dnUVZ8s-dnZ2d@pipex.net...
> "Baxter" <lbax02.spamguard@baxcode.com> wrote in message > news:129mdrmtivdop5a@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?
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
Baxter wrote:
> "Steve at fivetrees" <steve@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 (cbfalconer@yahoo.com) (cbfalconer@maineline.net) Available for consulting/temporary embedded and systems. <http://cbfalconer.home.att.net> USE maineline address!
On 2006-06-23, Baxter <lbax02.spamguard@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!
Baxter, 

Does every message comes with your SPAM?

"Grant Edwards" <grante@visi.com> wrote in message
news:129mnrf11vik1bd@corp.supernews.com...
> On 2006-06-23, Baxter <lbax02.spamguard@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.
"Mike Warren" <miwa-not-this-bit@or-this-csas.net.au> wrote in message
news:449b5c6e$0$490$61c65585@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.
On Thu, 22 Jun 2006 22:50:51 -0700, "Baxter"
<lbax02.spamguard@baxcode.com> wrote:

>"Mike Warren" <miwa-not-this-bit@or-this-csas.net.au> wrote in message >news:449b5c6e$0$490$61c65585@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.
Peter wrote:
> "Thad Smith" <ThadSmith@acm.org> wrote in message > news:449cbd18$0$233$892e0abb@auth.newsreader.octanews.com... > [snip] > >> As far as shortening hexadecimal to hex and getting confused, that what >> often happens with usage over time. I am guilty of abbreviating a mu, >> prefix for micro, with a similar looking Roman u. Some people probably >> think that "us" is the proper abbreviation for microseconds (uF, uV, uW, >> etc.). The ones that get me going are the use of capital S for seconds >> (SI symbol for Siemens) and K for kilo. >> >> -- >> Thad > > Of course you can use the correct abbreviation to deliberately confuse the > general public. I saw a model railway in a visitor centre with warnings > saying "Beware, High Voltage!!! 36,000mV". >
My grandfather (many years ago) told me of doing that, in the 1920's: "Danger! 4000mV" Kept the fingerpokers well away :)
"Thad Smith" <ThadSmith@acm.org> wrote in message 
news:449cbd18$0$233$892e0abb@auth.newsreader.octanews.com...
[snip]

> As far as shortening hexadecimal to hex and getting confused, that what > often happens with usage over time. I am guilty of abbreviating a mu, > prefix for micro, with a similar looking Roman u. Some people probably > think that "us" is the proper abbreviation for microseconds (uF, uV, uW, > etc.). The ones that get me going are the use of capital S for seconds > (SI symbol for Siemens) and K for kilo. > > -- > Thad
Of course you can use the correct abbreviation to deliberately confuse the general public. I saw a model railway in a visitor centre with warnings saying "Beware, High Voltage!!! 36,000mV". Peter
Steve at fivetrees wrote:
> "Baxter" <lbax02.spamguard@baxcode.com> wrote in message > news:129o3qqilr13v32@corp.supernews.com... > >>I understand it fine. However, for something like 20 years in my world, >>"Octal" meant an 8-bit value represented by a base-8 numbering system, >>while >>"Hex" means "Hexadecimal" which is a 16-bit value represented by a base-16 >>numbering system. I'm simply saying that, in my (software) environment, >>I'm >>used to "octal" being smaller than "hex". Thinking of it otherwise does >>not >>come natural. > > > I presume that was a typo.
I presume it was a thinko.
> An octal digit represents a 3-bit value. A > hexadecimal digit represents a 4-bit value.
Yes, but keeping more with the derivation, an octal digit can represent 8 possible values and a hexadecimal digit can represent 16 possible values. Back in seventh grade math class, we worked with base 7 and base 12 (septal and duodecimal?). As far as shortening hexadecimal to hex and getting confused, that what often happens with usage over time. I am guilty of abbreviating a mu, prefix for micro, with a similar looking Roman u. Some people probably think that "us" is the proper abbreviation for microseconds (uF, uV, uW, etc.). The ones that get me going are the use of capital S for seconds (SI symbol for Siemens) and K for kilo. -- Thad
"Baxter" <lbax02.spamguard@baxcode.com> wrote in message 
news:129o3qqilr13v32@corp.supernews.com...
> > I understand it fine. However, for something like 20 years in my world, > "Octal" meant an 8-bit value represented by a base-8 numbering system, > while > "Hex" means "Hexadecimal" which is a 16-bit value represented by a base-16 > numbering system. I'm simply saying that, in my (software) environment, > I'm > used to "octal" being smaller than "hex". Thinking of it otherwise does > not > come natural.
I presume that was a typo. An octal digit represents a 3-bit value. A hexadecimal digit represents a 4-bit value. But I bet you knew that, really ;). Steve http://www.fivetrees.com
Baxter wrote:
> I understand it fine. However, for something like 20 years in my world, > "Octal" meant an 8-bit value represented by a base-8 numbering system, while > "Hex" means "Hexadecimal" which is a 16-bit value represented by a base-16 > numbering system.
Hmm... Then how would you express 32-bit values? And 11-bit values? Sorry, couldn't resist, but it's Friday night anyway :) Vadim
"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:449BFADE.1A5A280F@yahoo.com...
> Ken Asbury wrote: > > pjberg@webtv.net wrote: > >> Baxter, > >> > >> Does every message comes with your SPAM? > > > > Not that I appreciate spammers any more than you do but, in > > the 6 years I've been lurking here, Chuck Falconer has been ... > > I don't think his message had anything to do with me, but rather > with the (perfectly permissable) mild advertising in Baxters > original sig. line. I suspect you are being confused by atrocious > threading in the google display. Berg is just confused. >
Exactly right. Berg is a stalker. I prefer not to engage him in technical forums, and leave any interactions with him to the entertainment (political) forums.
"Grant Edwards" <grante@visi.com> wrote in message
news:129o2db81kodmea@corp.supernews.com...
> On 2006-06-23, Baxter <lbax02.spamguard@baxcode.com> wrote: > > > 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. > > When the input pin on an open-drain/open-collector buffer is > low, the output pin is shorted to ground. When the input pin > on an OC/OD buffer is high, the output pin is not connected to > anything. If you want the "not-connected" output pin state to > be high, you have to connect a resistor between the output pin > and V+. >
Ok, now this starts making some sense. The input pins on the buffer are connected to the Serial output of a Palm. We're talking the RxD, TxD, RTS, CTS, etc.
"Grant Edwards" <grante@visi.com> wrote in message
news:129o27i9p0srpa1@corp.supernews.com...
> On 2006-06-23, Baxter <lbax02.spamguard@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. > > In that case "hex" his short for "hexadecimal". > > "Octal" means having to do with the number 8. "Hex" means > having to do with the number 6. "Hexadecimal" means having to > do with the number 16.
I understand it fine. However, for something like 20 years in my world, "Octal" meant an 8-bit value represented by a base-8 numbering system, while "Hex" means "Hexadecimal" which is a 16-bit value represented by a base-16 numbering system. I'm simply saying that, in my (software) environment, I'm used to "octal" being smaller than "hex". Thinking of it otherwise does not come natural.
On 2006-06-23, Steve at fivetrees <steve@NOSPAMTAfivetrees.com> wrote:
> "Rocky" <robert@suesound.co.za> wrote in message
>>> (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). >> >> errmm. Low = sourcing current.... :) > > Huh??
My reaction also... -- Grant Edwards grante Yow! There's a lot of BIG at MONEY in MISERY if you have visi.com an AGENT!!
"Rocky" <robert@suesound.co.za> wrote in message 
news:1151075230.722755.15310@c74g2000cwc.googlegroups.com...
> > Steve at fivetrees wrote: >> "Baxter" <lbax02.spamguard@baxcode.com> wrote in message >> news:129mdrmtivdop5a@corp.supernews.com... > Snip-a-Bit >> (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). > > errmm. Low = sourcing current.... :)
Huh?? Steve http://www.fivetrees.com