From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Ada for Automation Date: Fri, 7 Nov 2014 14:46:00 +0100 Organization: cbb software GmbH Message-ID: <3oth40wo6pbs.vs09ud18d1c8.dlg@40tude.net> References: <3e877e3f-c9ad-48a5-941d-08a7f5c3f317@googlegroups.com> <3wgqzq98u7gx$.17hpf52b2gd7l.dlg@40tude.net> <38980827-610e-42fc-a8bf-59a99bbdeee7@googlegroups.com> <1bbqo878nvb2p$.1n3uysmo360g3.dlg@40tude.net> <78b6c566-66a4-4275-ace0-be2f3553bc12@googlegroups.com> Reply-To: mailbox@dmitry-kazakov.de NNTP-Posting-Host: J8B/Z5QBLnsGuljexy5Hxw.user.speranza.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8bit X-Complaints-To: abuse@aioe.org User-Agent: 40tude_Dialog/2.0.15.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:23058 Date: 2014-11-07T14:46:00+01:00 List-Id: On Fri, 7 Nov 2014 03:44:38 -0800 (PST), slos wrote: >>> This you cannot do with, let's say, Modbus. >> >> Of course you can. There is no problem to query only data you needed over >> ModBus. We do this all the time. > No, that's not the same thing. > With today field buses you are able to select what will be exchanged > cyclically in a PDO (CANopen / EtherCAT / POWERLINK) or Assembly > (Ethernet/IP). EtherCAT does not do anything cyclically. The master must explicitly initiate every single cycle. It is strictly client-server. All immense configuration overhead and slave complexity could be spared if the master simply queried slave's registers using slave ID and the data point ID. > The device will prepare its answer accordingly. Which is unnecessary overhead only complicating EtherCAT masters and slaves. BTW, our master does not use FMMU and other useless stuff. Which is why it is capable to run as many independent cycles as needed, all simultaneously. It does not make sense querying temperatures and digital inputs at 200µs, right? > With Modbus, you can access of course the whole data set but you end up > reading more data and filter out the one you don't need or make several > requests to pick up only the data needed. No. This is maybe an artefact of the libmodbus you are using, I don't know it. But in ModBus (class 2) you can read/write any single register or any sequence of adjacent registers. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de