MODBUS and RS-485 are very commonly related and used together. As I remember RS-485 is just a format that goes farther distance than RS-232. This is/was typical in SCADA systems. I don’t recall if it was TTL logic levels or not. I would not be surprised if the cable is also a TTL logic converter.
Jamie can probably shed a lot more light on the topic. Thank you, Brian Webster www.wirelessmapping.com From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of ch...@wbmfg.com Sent: Wednesday, August 19, 2020 12:27 PM To: af@af.afmug.com Subject: [AFMUG] OT odd data connection On one of my large portable air compressors, there is a data port. They sell an adapter cable for about $200 It adapts it to USB. The program that you use to talk to it makes reference to modbus. The data port has 4 pins. RJ-10 4p4c connector. +5 with enough current to light an incandescent light bulb. +5 low current +5 low current Ground This sounds like USB host to me. One of my sons think it is RS-485 I don’t think USB would be happy on a RJ-10 and utp wire. Maybe it would. Maybe I am just buying a piece of wire with two connectors on the ends. The controller it plugs into is $2000 so I don’t want to experiment on that. Be interesting to see the adapter cable when it gets here. See if there are any active components. I would have probably just wired it up to a USB and tried it if my son had not made the modbus/RS485 comment. Any guesses?
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