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| 12/6/2011 5:34 PM | |
Joined: 1/17/2007 Last visit: 3/10/2025 Posts: 1557 Rating:
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You will not find a cable to connect a S7-200 Modbus connection to a PC Modbus connection. There is a very good reason for this. Most PC's have an RS-232 interface and the S7-200 has an RS-485 interface. These 2 interfaces are not compatible even though they look the same as they both use 9-way D type connectors. You will either need an RS-485 card for your PC (usually a PCI card of some type) or an RS-232 to RS-485 convertor. There are quite a few commercially available convertors, some require separate power supplies, but the best are powered via the RS-232 port and require no separate power supply. B+B electronics make several. I have used the 485SD9TB one in the past and it has worked fine. If using a PCI RS-485 card, you would have to check the pinouts for the card as there is no defined standard for RS-485 as there is with RS-232. You would then have to connect to the A/B or +/- or Hi/Lo pins on the card interface using a 9-way D Type. Different manufacturers have different designations for the interface pins, hence the A/B or +/- or Hi/Lo. Basically they are the same connections but with different names (A = + = Hi and B = - = Lo). If using a convertor, you would just use some loose wire connections. The Pin outs for the S7-200 are pins 3 (signal B) and 8 (signal A). These 2 connections should be connected to the B/-/Lo and A/+/Hi connections on the convertor or PCI card D type (depending on which you choose to use). Use any good quality 2 core twisted pair cable with an overall screen. Note: due to confusion with the RS-485 pin naming, it might be neccessary to swap over the connectors (signal A to B/-/Lo and signal B to A/+/Hi). There is no way to tell this in advance. First try in one way, and if it does not work try it the other way. It will not cause any damage to have it connected the wrong way round, it just will not work that is all. Good luck. |
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Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. |
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| 12/8/2011 5:57 AM | |
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Posts: 7 Rating:
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Thank you for the very comprehensive and useful information!
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