4/20/2016 8:40 AM | |
Joined: 4/28/2015 Last visit: 2/7/2024 Posts: 10533 Rating: (820) |
eeeeehm sry for long post maybe little addition, CRC isn't only Siemens side, it's standard implemented on many devices, communications. Study link: https://en.wikipedia.org/wiki/Cyclic_redundancy_check |
With best regards... |
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4/24/2016 3:02 PM | |
Joined: 4/28/2015 Last visit: 2/7/2024 Posts: 10533 Rating: (820) |
Hello Gerard, thnx for post. Yes, also on Profibus CRC is implemented, here you can look at some system on ProfiSafe, this kind of CRC calculation I was also implemented with one RFID communication: http://www.itk.ntnu.no/fag/TTK4545/TTK2/PDF/ProfiSafe-Profil-100e.pdf I think that you as programmer do not need to know how to calculate CRC on Profibus, because this is internal implementation, simply that communication work on network and in case of problem some diagnostic event will occur (f.ex. on CPU BUSF will light,...). I can agree, that CP card with 20mA TTY interface is suited against that interferences, but you can also use CRC if you decide to, also if other side device required it. To that your CRC calculation, it not must be big problem, as I said, there are examples to CRCs calculation. If you want to look at some LRC system, look here: http://www.simplymodbus.ca/ASCII.htm As you said about link provided to implementation of Modbus ASCII on CP340 is writen by our friend, his system can be probably used but look for first to that previous link, I think you can make it for yourself. With infos about Modbus automatic CRC calculation within library is only needed to know, that if you use that library (probably that you must pay for it, also f.ex. S7-1x00 CPUs free Modbus library), you don't need waste time with this, CRC will be calculated automatically and putted to frame on right place, therefore are prepared instructions that only needs basic input parameters, other work is automated. Probably for your ASCII Modbus, this is LRC calculation (previous link). With that color of some CP card, functionality is prefered Hope give you some other useful infos. |
Last edited by: Duris_I at: 4/24/2016 3:02:43 PMLast edited by: Duris_I at: 4/24/2016 3:04:39 PMWith best regards... |
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4/27/2016 9:15 PM | |
Joined: 10/5/2014 Last visit: 8/12/2022 Posts: 243 Rating: (1) |
Hey Duris, Thanks for your comprehensive explanation To sum op: for the crc i need the library (which is included if i buy the propiate siemens modbus module). or i need to make a complicated calculation myself. i get back to this later. As mentioned before: the 20ma current loop tty connection. i was also doing some study on this one and i came to the following https://support.industry.siemens.com/cs/attachments/7123872/7123872_RK512_DOKU_V1d0_en.pdf In this document for programming a 20ma tty connection, they refer on page 17 that the cpu should have 'something' for program modbus master and modbus slaves. (see figure 5-1). This sofware packet as mentioned, is that the same packet as i need in my library for the crc calculation. also in the document on page 12. there is a scheme of the fb's needed for program to a coupling partner. but in my library i cannot find fb 40 and fb 41 but i can find fb 2 and fb 3 i asume that fb2 and fb3 are the same as i use for the rs422/rs485 communication. how is this gr gerard |
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