VME - CAN4 Intelligent Board for 4 DeviceNet Channels for VMEbus
The VME - CAN4 is a VMEbus 6U board with 4 complete, independent CAN interfaces to the VMEbus and needing only one slot. Each interface is equipped with its own CAN micro controller 68331 with a 20 MHz clock frequency and a working memory of 256 Kbytes. After a RESET, the micro controller program code is loaded from the local Flash EPROM. Program updates can be loaded into the Flash EPROM via the VMEbus. The CAN data transfer from and to the VMEbus is performed via a shared 512 Kbytes RAM and FIFOs. Received Rx data generates a local interrupt, which is processed by the appropriate micro controller that stores the data in the shared RAM; the identifier is stored in the FIFO (FIFO to master). It then generates a VMEbus interrupt. For each of the four CAN channels an individual interrupt vector is generated. The VMEbus master transfers CAN data by entering the data into the Shared RAM and with this, an automatic pointer to the identifier is stored in the FIFO (FIFO to slave). The appropriate micro controller reads FIFO and RAM and starts the data transmission.
The VME - CAN4 includes a high-speed CAN controller SJA1000 supporting both the standard CAN protocol (11 bits identifier) and the extended CAN protocol (29 bits identifier). The physical CAN layer is fully ISO 11898 compliant with a maximum baud rate of up to 1 Mbit/s that can be programmed in a range from 10 Kbits/s to 1 Mbit/s via the VMEbus. The CAN channels are electrically isolated from each other as well as from the VME section, and four DC/DC converters supply the local power. esd electronics, Inc. guarantees a transfer rate of 1 Mbit/s for a bus length of 37 m, if the other CAN participants are equivalently equipped. Connection of the CAN nets is performed by 9-pole DSUB female connectors at the front panel, and a piggy-back interface is available for other layers or connector standards.
esd electronics, Inc. provides a LED display on the front panel showing the state of the CAN controller and of the micro controllers for each channel as well as the general board state.
The extremely error-tolerant CAN protocol (Hamming distance = 6) includes a standardized transfer frame and a high transfer rate and is highly suitable for the construction of decentralized I/O nets, where a safe and manufacturer-independent communication protocol is necessary because of the variety of the applications.
One essential advantage of the CAN protocol is its self-arbitration and multi master capability that provide the user the ability to interconnect in a CAN net various sensors, actuators, CAN I/O modules as well as VMEbus controllers, PCs, PLC modules or stand-alone controllers.
The integrated firmware enables communication opportunities at OSI layer 2 or with higher layer CAN protocols; by means of the shared RAM interface as well as the FIFO interface to the VMEbus section, a use of the board with various operating systems at layer 2 can easily be performed. Drivers for VxWorks, LynxOS and Linux are available. Basic functions, such as CAN monitoring or automatic interfacing of CAN nets are easy to parameterize. The standardized higher layer protocols CAL/CMS and CANopen are already available as master or slave package for nearly all operating systems, as well as complete software packages for SDS master operation and for DeviceNet. The firmware interface of the VME - CAN4 is compatible to the firmware of the VMECAN2.