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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"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
SN74LVC07A).
in
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.
buffers,
good.
is
aHere 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?
Octal buffers have 8 in one package.
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
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.
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Raises what issue? You do know that the prefix "oct" means eight, right?
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Baxter,
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buffers
I'm primarily a software guy - Octal means base 8 number - Hex is 16-bit number.
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
which
Now you are frightning me! How many sides has a hexagon got? And a decahedron? and finally a hexadecahedron? How many arms has an octapus? How many wheels does a 4WD RV have? OK, trick question, spare and steering makes six.
Peter
Open collector/drain outputs are useful for several purposes. For example:
o Drive a signal that can be driven LOW by more than one outupt. o Wire ORing. Similar to the usage above. Often used for interrupt signals. o LED drivers. The current through the LED is switched ON when the buffer/driver output is turned on to sink the current from the LED. o Level translation. The pullup resistor is tied to a voltage acceptable to the inputs it will be driving.
The point I am trying to make here is that there is likely a reason that these open-collector drivers are being used, and we cannot know the reason without understanding more about the circuit. I hope this helps.
-- Michael N. Moran (h) 770 516 7918 5009 Old Field Ct. (c) 678 521 5460 Kennesaw, GA, USA 30144 http://mnmoran.org "So often times it happens, that we live our lives in chains and we never even know we have the key." The Eagles, "Already Gone" The Beatles were wrong: 1 & 1 & 1 is 1
Paul Berg,
Not that I appreciate spammers any more than you do but, in the 6 years I've been lurking here, Chuck Falconer has been a valued contributor to this NG, bringing light, not heat, to every discussion I've ever seen him enter. In RF terms, he has a very high SNR (Signal-To-Noise-Ratio) in a NG that tends to have that same pleasant characteristic.
His signature line certainly is the least offensive form of self- promotion that I encounter on my daily dip into the internet, kind of like your "federal law enforcement (retired)" tag.
about a lot of things on a lot of NGs. Could I suggest that, IMHO, this NG doesn't need your protection from the likes of Chuck Falconer and, further, suggest that you move on to someplace that needs your talents more urgently?
With the greatest respect for you past contributions to the safety of the American public and my best wishes for a happy and productive retirement.
Ken Asbury
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.
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Available for consulting/temporary embedded and systems.
USE maineline address!
Snip-a-Bit
errmm. Low = sourcing current.... :)
Rocky
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.
After you were told that a "hex buffer" is a package that contains six buffers, you really couldn't figure out what an octal buffer was? Even when the data sheets for the parts show that a hex buffer package contains 6 and an octal buffer package contains 8?
BTW, there are also hex nuts (which have 6 sides), hex wrenches (6 faces), hexagons (polygons with 6 sides), hexapods (organism with 6 legs), hexane (hydrocarbons with 6 carbons), octal sockets (for tubes with 8 pins), octagons (polygons with 8 sides), octopuses (cephalopods with 8 tentacles), octave (a difference of 8 steps in music), October (the Eighth month in the original Roman calendar), octane (a hydrocarbon with 8 carbons), and so on.
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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+.
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[The description below is for a non-inverting buffer. I tend to assume a "buffer" is non-inverter, otherwise it would have been called an "inverter".] [...]
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Huh??
Steve
My reaction also...
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