yyrkoon

Implementing an I2C slave device.

27 posts in this topic

11 hours ago, zeke said:

Whoops. I forgot that detail. I must be getting old.

So this is I2C over CANBUS then. Sorta. 

I have never worked with CANBUS. Can it cover that distance at that speed?

 

It's I2C over CANBUS, exactly. I've been told by my buddy that I was wrong, that the carrier is actually 5v, and that the 24vdc is for power only. Not quite sure how that works with only two "lines"( single twisted pair over cat5e ). But yeah I do not recall how long a distance CANBUS can handle, only that at the time I was told, it seemed ridiculously long when you consider how long a car is. I do know that the software protocol is 1Mbits max, which I'm not exactly sure is applicable to this situation or not.

 

EDIT:

So maybe reverse logic coms ? e.g. offset starting at 24vdc minus 5vdc when pulled low/ high or something ? heh yeah I'm lost ;)

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Even at the highest speed (1Mbps) the spec calls out 40M max bus length. Good for stretch limos or buses I suppose.  :)

Here is a snippet from a CANBUS page ( http://www.interfacebus.com/CAN-Bus-Description-Vendors-Canbus-Protocol.html ):

"A number of different data rates are defined, with 1Mbps (Bits per second) being the top end, and 10kbps the minimum rate. All modules must support 20kbps. Cable length depends on the data rate used. Normally all the devices in a system transfer uniform and fixed bit-rates. The maximum line length is 1Km, 40 meters at 1Mbps. Termination resistors are used at each end of the cable. The worst-case transmission time of an 8-byte frame with an 11-bit identifier is 134 bit times (that's 134 microseconds at the maximum baud rate of 1Mbits/sec)."

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