On Mon, May 4, 2009 at 8:19 AM, solarwind wrote: > I understand that RS485 is a physical layer specification that, > according to one of Olin's posts is a "recommended standard" for > nothing more than the physical/electrical specifications of the > system. What's now confusing to me is what CAN is. I know that it is > at least a protocol, but is it anything more? Does it specify the > physical layer like RS485 does? The Wikipedia article on CAN is a bit > too difficult to understand for me at this stage. If anyone could put > it in simpler terms, I would greatly appreciate it. The CAN specification only specify a very small portion of the physical layer. This is a good website about CAN. http://www.can-cia.org/index.php?id=46 > How similar is the CAN bus physical layer specification to the RS485 > specification? Both are using differential signal. Both supports multi-drop. RS485 is only a physical layer specification. CAN has the data link layer specified and a bit of the physical layer specified. Both needs upper layer support, either open standard or proprietary. CANopen, DeviceNet, SDS > How many lines does the CAN bus usually use? At least three: CAN+, CAN-, and GND. Sometimes you have another 24V voltage, like the one in DeviceNet (based on CAN), actually we have one more line for DeviceNet: the shield. > > Can the bus lines from my CAN transceiver module be directly connected > to the twisted pair wires in a CAT3 or CAT5 cable and to other CAN > devices? You need termination resistor at the two end of the network. > What is "termination" (tried to google for it and got unexpected > results :P) and does the CAN bus need it? The CiA (CAN in Automation) website provides good information. Usually you use 120 Ohm. We used 121 Ohm in DeviceNet. > I'm thinking of making a simple PCB in the style of an ethernet switch > that will simply have a few RJ11 or RJ45 connectors connected to each > other. Nothing more, nothing less. Is this a good idea? Maybe not. -- Xiaofan http://mcuee.blogspot.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist