On Mon, 2012-02-27 at 19:48 +0000, Chris Morley wrote: > > > > > There may be a function that can look this up, but I think it's hard for > > the API to know what network the app needs to use, although 99% of the > > time the host has a single Ethernet port making the practical choice > > easy. I got the libmodbus 3 unit-test demo to work by just doing a > > ifconfig to to get my IP address and plugged that in. That's all that > > was needed. RTU over TCP is probably a different story. My LinuxCNC > > master could send queries just fine, but the unit-test slave isn't set > > up to return anything interesting. Successes for unit-test demo seems to > > be a lack of error messages. > > > > CL requires the address and the port number (9502 id default). > I somewhat understand the address but not really the port number. > Can you elaborate how you found this info? keep in mind I have > almost no knowledge of networks other then plugging in my ethernet cable > in to my cable internet router. :) > > Chris M
I'm not sure of the proper terminology and I'm learning as I go, but each network node or Ethernet connection has an address like 192.168.1.10, then services that can be provided on a network node have a port number. So when LinuxCNC makes a request it gets routed to the network card that has the proper address, then the card routes the request to the proper service by using the port number. If the request was for an HTML web page or FTP file transfer, the address would be the same but the port number would be different. ModbusTCP seems to have a default address of 502, but it really could be anything. Addresses above 1000 are handled with fewer restrictions, the libmodbus demo selects port 1502 so the demo doesn't need to be run as root. You can see active ports of services your computer is providing from the desktop here: System > Administration > Network Tools > Netstat > Active Network Services For libmodbus 3 it seems the slave address(es) needs to be determined and entered in both the master component, so the master knows which slave to talk to, and the slave driver, so the slave knows which Ethernet card and service port to listen to for requests. libmodbus has a feature called ModbusTCP/IP that can use a hostname to find the network address, but I haven't looked into it yet. There is another variation of ModbusTCP for using Ethernet to serial port bridges where the network information and the serial port information need to be included within the Modbus packet in order to find the proper slave. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Try before you buy = See our experts in action! 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-dev2 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
