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gip_mad
Joined: 23 Aug 2008
Posts: 24
Location: Italy
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| CAN data corrupt |
 Posted: Sat Aug 23, 2008 8:08 am |
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Hello,
I built a circuit with a 18lf2680 and Texas SN65HVD1040DR (the equivalent of MCP2551) to test the CAN bus at 50kbps. The board uses the internal oscillator @8MHZ and is connected to a LAWICEL CANUSB device (www.canusb.com).
I have the two 120ohm resistors in place.
I made a test project with the useful project wizard so the compiler selected the best parameters for the bus.
I see a strange behavior: the CAN monitor on my pc receives packets with the correct address but the data is completely different.
I tried both 29 and 11 bit identifiers, but the result is the same: I get 2 alternating set of data...
but the array that I write is always the same:
| Code: |
CCS CAN EXAMPLE
Running...
PUT 1: ID=2645 LEN=8 PRI=3 EXT=0 RTR=1
DATA = 01 02 03 04 05 06 07 08
PUT 1: ID=2645 LEN=8 PRI=3 EXT=0 RTR=1
DATA = 01 02 03 04 05 06 07 08
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I also tried to change manually the config registers, following PCM programmer's GREAT guide, but the result is the same.
| Code: |
BRGCON1 = 0x07;
BRGCON2 = 0xA1;
BRGCON3 = 0x01;
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Also the Address is received correctly, so I think my timing is correct (I tried with 0x55, so it is 01010101 and I can spot errors easily).
Do you have any suggestion?
Also, another question: this will be a battery powered device, and it must have very low power consumption. Is the CAN bus the right choice? The bus length will be about 80mt, and the anti collision will allow me to do some nice tricks. Will the module receive messages also when the PIC is sleeping, and wake him up? It needs the main clock, right?
Thank you very much
Cristiano |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Aug 23, 2008 11:17 pm |
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Try running the PIC board with the CAN bus in Loopback mode.
Disconnect the Lawicel CANUSB device, and just connect the PIC board
to the PC with a RS-232 connection:
http://www.ccsinfo.com/forum/viewtopic.php?t=20106
In the middle of this thread, there is a test program for two PIC boards,
with a CAN bus connection on each board. This code will test if the two
PIC boards can talk to each other correctly through the CAN bus.
http://www.ccsinfo.com/forum/viewtopic.php?t=29627
Both of these tests display the result in a terminal window on the PC.
The connection to the PC is made by RS-232. The reason for this
is because maybe your Lawicel CANUSB device and software don't work,
or the configuration of the software is incorrect. By using the tests
above, you can test your PIC board without using the Lawicel CANUSB
device. |
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gip_mad
Joined: 23 Aug 2008
Posts: 24
Location: Italy
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| Posted: Wed Aug 27, 2008 10:37 am |
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Thank you PCM! IT WORKS!
I'm very happy, and I surely own you a beer.
I first tried in loopback mode, with the code you supplied, and it worked. Then I commented the loopback mode line.... And the CANUSB read it correctly!
Turns out, the example from CCS uses this line for sending data:
| Code: |
i=can_putd(tx_id, &out_data[0], tx_len,tx_pri,tx_ext,tx_rtr); //put data on transmit buffer
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Well, I didn't notice that at the tx_ext variable was declared as 0... But on the second link you posted, they say that the standard init function works only with EXT IDs!!! Does CCS test their code before publishing? The Fat16 library didn't even compile because of a typo... After correcting it, it worked like a charm! 
Do you have any suggestion on the other questions?
| Quote: |
Also, another question: this will be a battery powered device, and it must have very low power consumption. Is the CAN bus the right choice? The bus length will be about 80mt, and the anti collision will allow me to do some nice tricks. Will the module receive messages even when the PIC is sleeping, and wake him up? It needs the main clock, right?
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