On Sun, 2008-01-27 at 14:44 -0800, Kirk Wallace wrote: > On Sun, 2008-01-27 at 15:53 -0500, Stephen Wille Padnos wrote: > > Hmmm. > > > > Interesting idea to just have coils and registers presented as pins. > > Then you'd only need to specify how many of each you want to access, > > along with the base address. It gets more complicated if you need to > > allow access to registers/coils in multiple discontiguous ranges. > > > > There's also a problem with multi-register values. Some devices can > > handle 32-bit values, which are generally composed of two 16-bit %Rxx > > values. I'm not sure if the spec tells you to use a certain > > endian-ness, so it may be necessary to be able to specify that as well. > > This is why I was thinking about a higher level spec for specific > > devices (ideally with a low-level core that's at least from common > > source code, and at best a single shared module). It would be much more > > readable in HAL to have a modbus.0.vfd.0.spindle-speed pin rather than > > having something like the inverse of a scale block to convert from float > > to whatever integer units the VFD uses, then possibly to split that into > > two 16-bit words for connection to modbus.1.register001 and > > modbus.1.register002. It would also be possible now that I think of it, > > to have a VFD module that converts from "engineering units" to whatever > > registers and coils the modbus interface provides. The downside is that > > you end up with a lot of HAL connections that aren't really useful, and > > can cause major problems if they're screwed up (imagine the oops of > > swapping the high and low words of a spindle speed, for example).
Opps, I changed my mind. The simplicity of only thinking about coils and registers just moved the necessary complexity to another area. Just like all other hardware, I think, a file is needed to interface the hardware's features to EMC, There are just too many variables to try to make a generic interface. So my latest thinking is to make a component, SJ200-mb-rtu with pins and parameters for the features I want to interface with EMC like "SJ200-mb-rtu.0.frequency-in", "SJ200-mb-rtu.0.run", etc. The SJ200 component would know that to write to a register, we start with a Modbus address number, function code of 0x06 (register write), 0x00 ( reg. addr. high, 2 bytes), 0x01 (reg. addr. low, 2 bytes), and pin value (2 bytes). This stream would then be placed in a message buffer for the Modbus program handling the desired serial port, Modbus would add a CRC to the end and send it. The buffer is a mystery to me. I think I saw in the HAL documentation that pins could be arrays. > I didn't want to have any device dependent features in the Modbus RTU > component. I was hoping that that would be up to mixing other components > to get the data into the proper form. The Modbus RTU component would > only handle assembling the packet, managing the communications protocol, > and handling communications errors. > > I am using the my VFD manual as a guide, and all of its registers are > eight bit. For 16 bit parameters, it uses two register addresses and no > floating point, such as: > > Func- | Name | R | Description | Reg- | Ra- | Res- > tion | | / | | ister | nge | olu- I was wrong here, the SJ200 uses 16 bit registers. The Modbus standard indicates a frame as: Slave | Function | Data | CRC Address | Code | | Check ---------------------------------------------- 1 byte | 1 byte | 0 to 252 bytes | 2 bytes So, for other Modbus devices the registers could be any number of bytes long up to 252 bytes. > > I should stop thinking about it, because it keeps getting more complex > > the more I do :) > > > > - Steve > > My brain is is hurting, too (easy to do though). > > -- > Kirk Wallace (California, USA -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
