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'[PIC]: MCP2510 woes'
2001\08\18@203008 by Brandon Fosdick

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Ok, so I have my MCP2510's now and I've wired them up to a pair of
16F877's and TI UC5350 tranceivers, which claim to be pin compatible
with the Philips 82C250 that the appnotes like so much. I got the TI
part because Digikey doesn't sell the Philips tranceiver and I didn't
feel like paying the extra shipping for a seperate order. The datasheets
look the same to me.

Anyway, I can't get the thing to work. Is anybody else working with a
CAN system using the MCP2510?

I'm pretty confident in my code since it works beautifully with the
MCP2510 in loopback mode. I can make a PIC send and receive packets to
itself all day long. But as soon as I hook two devices together and set
it to normal mode it all goes to hell. REC on the receiving node goes
through the roof very quickly and none of the messages come through.

If I set it to listen only mode, I can see the packets coming across,
but they're all zeros, not the actual values that are supposed to be
sent.

Physically the setup involves two proto boards each with a 16F877,
MCP2510 and UC5350. One of them also has a MAX232 hooked to the USART
for displaying debugging text. The two boards are seperated by about 6
inches of wire that makes up the CAN bus. I connected CANH to CANH and
CANL to CANL with a 150 Ohm resistor across the wires. Not sure what
else to do.

If anybody has any experience with this, or wants more info, please let
me know. I'm stumped.

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2001\08\20@021726 by Chris Carr

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Brandon Fosdick wrote :
> Physically the setup involves two proto boards each with a 16F877,
> MCP2510 and UC5350. One of them also has a MAX232 hooked to the USART
> for displaying debugging text. The two boards are seperated by about 6
> inches of wire that makes up the CAN bus. I connected CANH to CANH and
> CANL to CANL with a 150 Ohm resistor across the wires.

Passive Termination of the bus should be done with a 120 ohm resistor at
each end of the cable. (you will note the tests on the Datasheet are done
with a 60 ohm resistor). I doubt that this is actually your cause of your
problem but there is always a remote chance that it could be.

I didn't know that TI did CAN Transceivers, it looks like a browse of their
site is overdue.

Regards

Chris Carr

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2001\08\20@122753 by Brandon Fosdick

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Chris Carr wrote:
>
> Brandon Fosdick wrote :
> > Physically the setup involves two proto boards each with a 16F877,
> > MCP2510 and UC5350. One of them also has a MAX232 hooked to the USART
> > for displaying debugging text. The two boards are seperated by about 6
> > inches of wire that makes up the CAN bus. I connected CANH to CANH and
> > CANL to CANL with a 150 Ohm resistor across the wires.
>
> Passive Termination of the bus should be done with a 120 ohm resistor at
> each end of the cable. (you will note the tests on the Datasheet are done
> with a 60 ohm resistor). I doubt that this is actually your cause of your
> problem but there is always a remote chance that it could be.

I'll try using another resistor. I planned to do that in the final
version, but figured since the prototypes are only 6" apart that I could
get away without it for now. At this point I'll try just about anything.

> I didn't know that TI did CAN Transceivers, it looks like a browse of their
> site is overdue.

http://focus.ti.com/docs/browse/productnavigation.jhtml?familyId=540&tfsection=products&templateId=5

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'[PIC]: MCP2510 woes'
2001\09\02@213532 by Brandon Fosdick
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I set the project down for a week or so and when I came back, I found
the problem. Turns out there was a very small peice of solder bridging
CANL and Vcc. I had inspected all of the connection several times, but
never with a magnifying glass. It was a very small peice of solder.

Thanks to those who tried to help.

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