Apparently modbus is a data protocol, not a physical layer standard, but yes it could go over RS485. I don’t see how a simple cable could convert from USB to RS485. I sure hope for $200 you are getting a dongle, not an expensive cable.
The connector you are referring to, is that a 4 pin modular plug, like used on the handset cord for a phone? From: AF <af-boun...@af.afmug.com> On Behalf Of ch...@wbmfg.com Sent: Wednesday, August 19, 2020 11:27 AM 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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