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发表于：2002-10-14 16:28:00

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Our group is building an adapter to communicate on DeviceNet and J1939 over the same wires. Can we safely make the statement that if we meet DeviceNet physical media Specifications, we will be meeting J1939 Specifications also?
Answered by Cyrilla Dalstra, Conformance SIG Member,
e-mail:
A49) It depends on what physical layer for J1939 that you are specifying. J1939 has 3 or 4 approved physical layers currently. DeviceNet is similar to the J1939/11 physical layer (which is the most popular). The John Deere physical layer J1939/12 is not similar at all.
Device Level: J13939/11 and DeviceNet are both based on ISO 11898 (which typically means using an off-the-shelf transceiver). DeviceNet requires opto-isolation and powering the transceiver from the network. This is not needed for J1939. J1939 is not a plug-n-play bus; also there is no "common power" to draw upon. For a flexible application, we typically design the device as a configurable system to turn this feature on or off (either by hardware or through software). Also, the device Bit Timing Registers (BTRs) are not typically configured the same.
System Level: They do not have the same requirements physically. DeviceNet has three different networks - 125K, 250K, 500K. They have varying bus lengths and drop length totals. In J1939/11, the baud rate is 250Kbps. The bus trunk length is 40m and drops can only be 1m. The number of nodes is limited to 30. The "media" is different as well. J1939 does not use any of the connectors or cables that DeviceNet uses. J1939/11 designates a triangular connector or a 6-pin Deutsche connector. The J1939/11 cable is also only 3-wires (CANH, CANL and shield).
You can not run the two networks on the same wire simultaneously. J1939 uses 29-bit identifiers while DeviceNet is 11-bit only. There are a lot of DeviceNet products that will not tolerate 29-bit IDs on their network - so do not mix the two.

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