1/19/2019 6:04 PM | |
Joined: 12/18/2014 Last visit: 9/24/2024 Posts: 33827 Rating: (4203) |
A found a german manual for a JUMO device. I attached a page of this manual. The german text translates Google as follow: 6.8 Distinction between MOD bus / J bus The MOD bus protocol is compatible with the J-Bus protocol. The difference between MOD bus and J bus is that the absolute
Attachmentsh70.4040d_page_26.pdf (249 Downloads) |
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1/28/2019 4:04 PM | |
Joined: 3/28/2010 Last visit: 9/21/2024 Posts: 1056 Rating: (213) |
There's a short two page note by Schneider (who now owns the former Modicon, author of Modbus). I could not locate the paper on the Schneider site, but its total contents are displayed here: https://studylib.net/doc/7686279/title--differences-between-jbus-and-modbus-protocols In reality, there's precious little difference between JBUS and Modbus. In register addressing, some Modbus vendors use zero based addressing or indexing (sometime documented as hexadecimal) and others use one based addressing (generally documented as decimal based). The latter is what JBUS formally adopts. The differences in limits in processing capacity are nearly insignificant. JBUS has a list of mandatory commands, all of which are defined in the Modbus spec, but I can't recall Modbus requiring any specific command set. With Modbus, you get what you get.If you're familiar with Modbus, implementing JBUS should be 'transparent', as the jargon goes nowadays. EDIT: It just occurred to me that the binary address in a JBUS telegram/packet might actually be one number higher than the equivalent Modbus address. For example a Modbus address 0A (hex) might be 0B (hex) in JBUS. The zero-based vs one-based one offset" issue with Modbus is an interpretation issue, how does one interpret the documented register addressing in light of the tools used to implement Modbus. In Modbus, a zero-based address or a one-based address use the same binary value in the telegram/packet. But I've never worked with JBUS devices, so I've never seen an example of theactual binary traffic to see whether that's the case or not. All that matters is whether the binary value is correct for the device receiving it. |
Last edited by: danw at: 1/28/2019 4:14:18 PM |
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