RS-422/485 MDrive products can appear to have a communications failure when it is merely in a mode that prevents it from responding to or echoing back, instructions in SEM Terminal.

Settings that can cause this include

  • Party Mode (PY=1)
  • Checksum (CK=1)
  • Echo Mode (EM=1or2)
  • Incorrect Baud Rate (BD)

Also, check the scroll bar in the terminal window. If it is not all the way down, you may not see what the driver sends back.

When you have communications problems, the simplest fix may be to set your driver back to factory defaults using the instruction “FD”. To prevent defaulting all the drivers in your system, you may want to plug your communications cable into only the driver you are working on.

Make sure that you have a backup copy of the all variable settings and program before doing this.

By inserting a string of text into one of the function keys in a Terminal window in SEMTerminal, it can be sent to the driver as a continuous string of characters:

(copy / paste string above) To do this, open SEM Terminal and click on the terminal window. If there is no terminal window open, open one using View > New Terminal Window.

Figure 1: Terminal window showing function key group

Right-click on the function key area at the bottom of the terminal window. The function key setup dialog will open.

Figure 2: Function key setup dialog
Pick one of the function keys and type something like “Reset FD” into the Caption. Then highlight, cut and paste the character string given above into the Contents window of that row and click on Done. When that function key is pressed, the string will be sent. Note that there are delays in this string and it takes about 4 seconds to complete. When you are able to communicate with the driver, type “S” then a carriage return. This will save the defaults.

If you still haven’t established communications, try setting SEM Terminal to different baud rates. This is done by Right-clicking the text area of the terminal window and select Preferences.

Figure 3: Terminal settings dialog
Figure 3: Terminal settings dialog

 

Then select the Comm Settings tab. Select the baud rate desired and make sure that the radio button for MDrive is selected. Select Done, then try your function key. You may have to try all the possible baud rates.

USB to SPI converter

The MD-CC30x-001 USB to SPI converter is a plug-n-play device, which uses a Virtual COM Port (VCP). Drivers will typically automatically install on an Internet connected PC, notebook or Windows tablet when the device is connected to a free USB port. If automatic installation fails, or if you need to download drivers for a non-connected PC, or for an alternate operating system, the drivers may be downloaded from the web at: Silicon Labs CP210x USB to UART Bridge VCP Drivers

Driver Installation (Automatic)

On an Internet connected Windows PC or Notebook, plug the MD-CC30x-001 into an open USB port on your PC.

The device driver software should automatically install.

 

Driver Installation (Manual)

Download the Silicon Labs CP210x USB to UART Bridge VCP Drivers from the Silicon Labs web site (will open in a new browser tab).

Extract the driver *.zip file to a location on your PC.

Double click the executable file appropriate to your operating system x86 (32-bit) or x64 (64-bit).

Follow the dialogs and prompts to install the drivers.

 

Verify installation (Windows 7/8.x)

Record the COM port number for later use, either from the notification balloon on the lower right of your desktop, or from the Windows device manager, accessible by right-clicking on “My Computer” and selecting manage (Windows 7) or by pressing the WIN+X keys on your keyboard (Windows 8).

What is noise?

“Noise” or “Interference” consists of unwanted electrical signals which superimposes on and masks the desired signal. Designing a control system is challenging enough, but designing a control system that has noise immunity adds a whole other dimension. Ideally, you want the noise-to-signal ratio to be as small as possible. Noise is always present in a system that involves high power and small signal circuitry. The key is to manage the noise so that it does not interfere with the performance of the system at hand.

 

Sources of noise

Sources of noise can be external to the stepper motor system as well as within. The most common external sources are relays and motors. Internally, the relatively high current motor drivers are the source. All bi-polar stepper motor drivers apply a chopping function to the applied voltage of each phase. This chopping enables use of higher voltages than the motor is rated for, achieving higher speeds while keeping the motor from getting too hot. The combination of the chopping and inductance of the motor creates noise on the ground plane. This [ground plane noise] can be introduced into nearby external systems if proper wiring and shielding precautions are not taken. The result can be intermittent failures of the system as a whole.

Components of noise and how to manage them
In order to manage noise it is important to understand its components. Noise [Interference] is categorized into two groups: radiated and conducted. Radiated interference is transmitted by electromagnetic fields and picked up by the antenna effect of other equipment. If it were always possible to isolate susceptible receivers and radiating sources from one another, radiated interference would be more manageable. As distance increases, radiation fields become weaker thus energy becomes dampened along a conduction path. Unfortunately with today’s limited system real-estate, distance isn’t usually an option. Reducing the antenna effect and adding shielding, controls this type of interference. (Improper shielding can cause more problems than no shielding at all. (See Wiring and Noise Shielding Best Practices.)

Conducted interference is that which is introduced into a circuit by either direct or indirect coupling. Both direct and indirect coupling are classified into three specific types: Resistive, Capacitive, and Inductive. These types of coupling are most frequent where common return circuits and power supply grounds exist. Conducted interference can originate from a variety of sources, such as relay and switch contacts, fan motors, power switching or digital devices with short rise and fall times. The effect of conducted interference cannot be eliminated as easily as shielding eliminates the effect of radiated interference. Good wiring practices are necessary to minimize Conducted interference. Give close consideration to connections to and from power supplies. Give particular attention to common grounds. Ultimately, the whole system must be referenced to them. (See Wiring and Noise Shielding Best Practices.)

How to detect noise

The first step in troubleshooting a noise problem is acquiring the right tools for the task. An isolated Oscilloscope is the chosen tool for detecting noise. A battery powered scope [if one is available] achieves the best circuit isolation, however a scope with an isolated ground will still be an effective tool. Also, keep in mind that a Digital scope may mask the noise depending on it’s sample rate and frequency response. Therefore, an Analog Oscilloscope is better than a Digital scope for detecting asynchronous signals of high frequency such as noise. Along with the scope, a wiring diagram and a basic knowledge of the systems operation are the best tools. The next step is to simplify the system. Start by removing power; then disconnect all system components from the Stepper driver that are not absolutely necessary for basic motion. Keep an open mind, even experiment a little by using a jumper wire to introduce noise and simulate the failure mode you are experiencing. Remember there may be more than one noise source.

SEM encourages our customers to ask questions and take advantage of our Application Support Team early in your design. We can review your system and make suggestions on the interfacing and wiring practices. We may suggest other tips that are application specific, but as a starting point refer to Wiring and Noise Shielding Best Practices for the basic rules.