Demonstration 3: Accessing CANopen Devices via the Internet by means of the JRCC System

During this demonstration you will use a Java applet to retrieve and modify the status of two CANopen I/O modules installed at Fachhochschule Reutlingen via the Internet (see Figure 1).


Figure 1: System setup

We connected the output lines of one of the I/O modules with its input lines and a fieldbus display spelling the German word 'FELDBUS' (see Figure 2).


Figure 2: The I/O module connected to the display

The JRCC client can now be used as an interface to this display. When an output line is switched to high, the corresponding letter of the display is lit and because of the feedback lines, the corresponding input line is also switched to high. Since the input and output lines are mapped to specific CANopen device profile entries (0x6000 and 0x6200, respectively), writing resp. reading these values provides full control over the display. In order to get a visual feedback of the current display status we further installed an interactive Web camera which delivers pictures of the display and the status LEDs of the I/O module.

In the same way, the JRCC client can be used as an interface to a CANopen analog Volt input node or the drives of a robot (e.g. an iselAutomation portal robot which will be added to the system in the near future) without any code modification.

Introduction to the Java Remote CAN Control (JRCC) Client

The JRCC client is automatically started while this web site is loaded and appears as a separate Java applet window on your desktop.

JRCC Usage:

1. Node Selection

The menu 'CAN-Nodes' lets you select a specific CAN node you wish to access. All further device access refers to this node until a different node is selected. When the selection is done, the corresponding Electronic Data Sheet (EDS) is automatically loaded from the JRCC server and displayed in the EDS Browser component on the left side of the JRCC client window.

2. The Electronic Data Sheet (EDS) Browser

The EDS Browser component at the left side of the JRCC client window provides convenient access to the information contained in the EDS file of a given CANopen module. The root node of the EDS tree is marked with the name of the EDS file. By double-clicking on an individual folder icon you can expand or collapse the corresponding entry in the EDS tree. By double-clicking on an individual entry (index or sub-index) the corresponding values are transferred to the 'Index' and 'Subindex' text fields at the right side of the JRCC window, identifying a specific device profile parameter of the selected CANopen module.

3. Device Profile Access

The buttons 'Read' and 'Write' let you retrieve and modify the device profile entry specified by the 'Index' and 'Subindex' text fields. The 'Data' text field contains the unparsed bytes of data as the were read from the CAN (cf. CANopen Byte Ordering). The 'Value' fields display the actual value according to respective representations (like hex, dec, ...). The data type (Unsigned8, Unsigned16, ...) is identified by the corresponding selection lists.
The communication is done by using the CANopen Service Data Object (SDO).

4. NMT Services

The menu 'NMT-Services' provides access to the actual CANopen bus state of the selected CANopen node. An overview of the state transitions is given here.

5. Server Arbitration

The JRCC Server at ROBO16.FH-Reutlingen.de grants exclusive access to only one JRCC client at a given time, in order to prevent confusing client interactions on the CANopen module. So when the JRCC client tries to contact the JRCC server, it is possible that the server is busy, serving a different client. After a fixed time period a connected client looses its connection to the server in order to allow other clients to contact the server. This can be done by using the 'Reconnect Server' option of the 'Applet' menu.

 

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