CAN on the 18F4680

sholto · Joined: 22 Mar 2006 Posts: 2

I am using PCWH 3.236 via ICD-U40 on a 18F4680.

The CAN drivers provided with the compiler don't seem to work. There is no output from the Tx pin on the device.

I wrote some of my own routines. In loopback mode the data transfers correctly from Tx to Rx buffers.
Additionally I now get a CAN packet out of the Tx pin at the correct baud rate.

However it is all zeros despite the data registers showing as loaded with valid data. The only transitions I see on a CRO are the CAN state changes to maintain clock sync.

Is there some starnge register somewhere that needs to be enabled particularly for this device? Here's what I did.

can_set_mode(CAN_OP_CONFIG);
BRGCONn set to 125Kb/s
CIOCON.endrhi = pull Tx high;
CIOCON.cancap = enable receive;
ECANCON.mdsel=fifo;
BSEL0 = make all RX/TX buffers RX;
can_set_mode(CAN_OP_NORMAL);

Fill the TXB0 address's and set it to extendedid.
Fill the TXB0 buffer data and set data length (8);
Set TXB0CON priority to 3;
Set the TxRequest bit for only TXB0CON;
I now see an all zeros CAN packet at the right baud rate.

Regards,
Sholto Weir.

jma_1 · Joined: 08 Feb 2005 Posts: 147 Location: Wisconsin

Greetings,
You mentioned the compiler examples do not work. I do not have the same compiler version and the latest example files. The CAN-18xx8 example file perhaps needs to be tweaked for the part which you are using? One troubleshooting suggestion might be to try and get the example code working correctly with your part or see if there updated examples.

Cheers,
JMA

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

What's the part number of the CAN bus transceiver chip
that you're using ?

newguy · Joined: 24 Jun 2004 Posts: 1903

andrewg · Posted: Fri Mar 31, 2006 9:40 am

"#define CAN_ENABLE_DRIVE_HIGH 0" is correct for the Microchip 2551 transceiver. Given that you're using Microchip PICs, defaulting to a configuration for the Microchip CAN transceiver seems quite appropriate to me, and not a bug at all.

As you've noticed, if you use a different transceiver, the CCS code is designed to allow their defaults to be overridden as required...
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Andrew

newguy · Joined: 24 Jun 2004 Posts: 1903

andrewg · Posted: Fri Mar 31, 2006 10:35 pm

I think I see your point. I didn't see any problems because it all worked for me "out of the box". Driving high would still work with the MCP2551, but also allow transceivers like the LT1796 which don't have pullups to also work without needing to override the default.
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Andrew