On 06/09/2014 10:05 PM, Gregg Eshelman wrote: > On 6/9/2014 7:10 PM, Kirk Wallace wrote: >> On 06/09/2014 05:48 PM, Trần Ngọc Quân wrote: >>> Hello, >>> Serial is slow, but it fast enough for on/off spindle, water pump; read >>> from emergent stop button, limit switch etc. >>> So can linuxcnc combinate lpt (and other ones) with com port? >>> >> >> I would suggest using Modbus. Serial R232 to RS484/422 adapters are >> common. LinuxCNC supports Modbus in ClassicLadder or with Python and >> LibModbus. Modbus is designed for machine control and is common on VFDs >> and with microcontrollers. Search the LinuxCNC wiki for Modbus for more >> information. > > So it can use an RS232 connection to a VFD to control on/off fwd/rev, > while everything else is running through a different control board?
It's not clear to me what the original post was asking. Generally, if I were to use the PC's serial port for I/O control, I would use Modbus. It is designed for industrial control. It has decent speed over long distances in noisy environments. This can not be said for USB, I2C, or the other popular PC based serial systems. Most VFD and PLC units have Modbus features. Also an Arduino or other micro-controller can be used for all sorts of analog, digital and PWM I/O. For a VFD, the advantage of Modbus over simple digital I/O is in being able to do more than the control of speed and direction. One can also monitor; voltage, load, frequency and other status features. Features can also be set or modified if needed. There was a hint of using the parallel port with serial, or using the parallel port for serial communications. Both of these are possible. LinuxCNC has no problem mixing signals from different ports for the same application. Such as using parallel port pins and an FPGA signal generator for a tool changer. For serial data from a parallel port -- early in my study of Modbus I used a few parallel port pins to bit bang the serial data to my VFD. It worked fairly well but is not the best way to go. There is also documentation in the Wiki describing how to use serial port pins such as RTS, DTS, and such for digital I/O. The advantage here is that these pins run at +/- 12 volts for better noise immunity if needed. The above assumes one has the skill to write software in order to customize what LinuxCNC has to offer. Otherwise, one would need to study the existing configurations to see if one of them matches one's requirements. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ HPCC Systems Open Source Big Data Platform from LexisNexis Risk Solutions Find What Matters Most in Your Big Data with HPCC Systems Open Source. Fast. Scalable. Simple. Ideal for Dirty Data. Leverages Graph Analysis for Fast Processing & Easy Data Exploration http://p.sf.net/sfu/hpccsystems _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
