On Tue, 2012-02-28 at 13:27 -0500, Stephen Dubovsky wrote: > We use modbus & modbus/ip in our products here. For IP, you need both an > ip addr/port AND the modbus slave address. Each device can have > 240-something addresses. Think of an IP to RS485 bridge (moxa and others > make them). I can talk to any of the slave devices by their modbus address > though one (the bridge's) IP addr/port. > > Modbus/IP is just a wrapper for a RS232/485 modbus packet. > > Stephen
Just to clarify a little (or create confusion if I got this wrong), Modbus RTU, Modbus ASCII and Modbus over TCP/IP do need a slave address because the end point is a serial device (the IP address and port is for the gateway or bridge device). Modbus TCP does not use a slave address, or rather, the slave address is the IP address and port number (often omitted if using the default of 502) since the end point is an Ethernet device. It seems that Modbus over TCP/IP setups are more common in the wild than end to end Ethernet Modbus TCP/IP, but if one where to set up LinuxCNC as a Modbus slave (currently only TCP/IP), it would be one of those exceptions. It's good news/bad news. The good news is, Modbus has a lot of options, the bad news, Modbus has a lot of options. http://en.wikipedia.org/wiki/Modbus#Protocol_versions -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
