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For remote access to CANopen systems
via telephone line
CANmodem is an intelligent gateway that allows remote access to CANopen systems via a conventional AT compatible modem.
The programming interface for Windows 2000/XP (API) provides functions for transmitting and receiving SDO messages as well as for configuration of the CANmodem. PC-based service and monitoring programs can simply access the CANmodem by means of the API via a telephone dial-up connection.
The CANmodem is a full CANopen node and has an object directory, two server SDOs and 127 client SDOs. Data of any length can be read and written via the client SDOs (segment size via Modem is 231 bytes). The module can act as a heartbeat producer and as a heartbeat consumer, can monitor up to 16 devices, and can transmit corresponding events in the CANopen network such as NMT events or heartbeat events. In addition, transmission and reception of any layer 2 messages is possible. This function can be used for transmitting and receiving any PDOs or for using the CANmodem with any CAN protocol.
In the event of service, many SDO accesses to the individual devices occur. The API not only allows SDO accesses to be initiated individually, but it also allows an entire list of SDO accesses to be initiated and transmitted to the CANmodem. This list is then processed locally by the CANmodem and the results are then returned. With many SDO accesses, the propagation time via the telephone line plays a minor role.
The CANmodem can be connected to a conventional, external AT-compatible modem either via the full-duplex RS232 interface or directly to the PC. Communication occurs through a serial protocol based on the HDLC standard. For modem adaptation, a configurable init string can be saved in the object directory.
Connection between the PC and the CANmodem is made by means of a safe callback procedure. For this, the caller gives the CANmodem his callback number, which is then checked by the CANmodem against a prespecified white list. If the relevant number is entered in the white list, the modem calls the caller back and starts an authorization phase based on the CHAP protocol. After successful authorization, the PC application can run all functions on the CANmodem.