I'm working on developing a DeviceNet product, and I've a
feeling I'm in deep trouble when reading the DeviceNet spec.
In one section the authors refer to "8-bit octets", "16-bit
octets", and "N*8-bit octets".
WTF?
The word "octet" was introduced to mean a chunk of _exactly_ 8
bits so that the word "byte" could denote a architecture
dependant chunk containing a quantity of bits other than 8.
I don't have a good feeling about this spec...
--
Grant Edwards grante Yow! Have my two-tone,
at 1958 Nash METRO brought
visi.com around...
DeviceNet has 16-bit wide "octets"!
Started by ●April 6, 2004
Reply by ●April 6, 20042004-04-06
In article <4072d059$0$17251$a1866201@newsreader.visi.com>, Grant Edwards <grante@visi.com> wrote:>I'm working on developing a DeviceNet product, and I've a >feeling I'm in deep trouble when reading the DeviceNet spec. >In one section the authors refer to "8-bit octets", "16-bit >octets", and "N*8-bit octets". > >WTF? > >The word "octet" was introduced to mean a chunk of _exactly_ 8 >bits so that the word "byte" could denote a architecture >dependant chunk containing a quantity of bits other than 8. > >I don't have a good feeling about this spec...Although I don't have the DeviceNet spec handy, I suspect it's either a typo or a misunderstanding by the tech writer. An octet is an 8 bit chunk. Just keep this in mind as you read the rest of the spec. If your gut tells you something different than the words, your gut may be right. ========= For LAN/WAN Protocol Analysis, check out PacketView Pro! ========= Patrick Klos Email: patrick@klos.com Klos Technologies, Inc. Web: http://www.klos.com/ ==================== What goes around, comes around... =====================
Reply by ●April 6, 20042004-04-06
On 2004-04-06, patrick@klos.com <patrick@klos.com> wrote:>>I'm working on developing a DeviceNet product, and I've a >>feeling I'm in deep trouble when reading the DeviceNet spec. >>In one section the authors refer to "8-bit octets", "16-bit >>octets", and "N*8-bit octets".[...]> Although I don't have the DeviceNet spec handy, I suspect it's > either a typo or a misunderstanding by the tech writer. An > octet is an 8 bit chunk.Judging by the rest of the section, the text in question should have been using the word "character" rather than "octet". The diagrams and examples are clear enough. Apparently I just got lucky in picking that particular paragraph as a starting point.> Just keep this in mind as you read the rest of the spec. If > your gut tells you something different than the words, your > gut may be right.-- Grant Edwards grante Yow! I like the IMPUDENT at NOSE on that car... Are you visi.com a TEEN-AGER?
Reply by ●April 6, 20042004-04-06
On 06 Apr 2004 15:44:25 GMT, Grant Edwards <grante@visi.com> wrote:> The word "octet" was introduced to mean a chunk of _exactly_ 8 > bits so that the word "byte" could denote a architecture > dependant chunk containing a quantity of bits other than 8.I've seen in some documentation in French (CAMAC controller, ATAT-based ;) `octet' was used for `byte', wich did pretty make sense there. Vadim
Reply by ●April 6, 20042004-04-06
On 06 Apr 2004 15:44:25 GMT, Grant Edwards <grante@visi.com> wrote:>I'm working on developing a DeviceNet product, and I've a >feeling I'm in deep trouble when reading the DeviceNet spec. >In one section the authors refer to "8-bit octets", "16-bit >octets", and "N*8-bit octets".Ah, Allen-Bradley. I want to find whoever decided to call their DeviceNet/ControlNet derived TCP/IP protocol "Ethernet/IP". It doesn't have to run on Ethernet, and IP stands for "Industrial Protocol". Great, no confusion there with anything else. It was hard enough to try and move Ethernet onto the factory floor with these AB/Rockwell guys coming in and confusing everything. -- Alex Pavloff - remove BLAH to email Software Engineer, ESA Technology
Reply by ●April 6, 20042004-04-06
> I've seen in some documentation in French (CAMAC controller, ATAT-based ;) > `octet' was used for `byte', wich did pretty make sense there.AFAIK octet /is/ French for byte, though. I'm not aware of another word for it.
Reply by ●April 7, 20042004-04-07
larwe@larwe.com (Lewin A.R.W. Edwards) writes:> AFAIK octet /is/ French for byte, though. I'm not aware of another > word for it.I believe it, and seem to recall it being explicitly chosen to avoid the proliferation of English derived words. Except that "octet" is not a synonym of "byte" anymore than "kilometre" is a synonym of "the distance between two road markers." Although talking about 16-bit octets should be no more incongruous than the phrase "John Cage's microtonal notes resulted in 84 tones to an octave." -- Darin Johnson Caution! Under no circumstances confuse the mesh with the interleave operator, except under confusing circumstances!
Reply by ●April 7, 20042004-04-07
In article <bnb670dninlure8jg4issu5uu08vfuru6t@4ax.com>, Alex Pavloff wrote:> On 06 Apr 2004 15:44:25 GMT, Grant Edwards <grante@visi.com> wrote: > >>I'm working on developing a DeviceNet product, and I've a >>feeling I'm in deep trouble when reading the DeviceNet spec. >>In one section the authors refer to "8-bit octets", "16-bit >>octets", and "N*8-bit octets". > > Ah, Allen-Bradley. I want to find whoever decided to call their > DeviceNet/ControlNet derived TCP/IP protocol "Ethernet/IP".:) Anybody who uses "IP" in a networking context and doesn't mean Internet Protocol is just begging for a big L on their forhead.> It doesn't have to run on Ethernet, and IP stands for > "Industrial Protocol". Great, no confusion there with > anything else. It was hard enough to try and move Ethernet > onto the factory floor with these AB/Rockwell guys coming in > and confusing everything.Try PROFInet: that way you can add the fun of badly translated documents... -- Grant Edwards grante Yow! PEGGY FLEMING is at stealing BASKET BALLS to visi.com feed the babies in VERMONT.
Reply by ●April 7, 20042004-04-07
In article <bnb670dninlure8jg4issu5uu08vfuru6t@4ax.com>, BLAHalex@BLAHpavloff.netBLAH says...> It doesn't have to run on Ethernet, and IP stands for "Industrial > Protocol". Great, no confusion there with anything else. It was hard > enough to try and move Ethernet onto the factory floor with these > AB/Rockwell guys coming in and confusing everything...you mean, that wasn't their intention all along? --Gene
