LPC1768 CAN DLC problem

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by jchisolm on Wed Nov 02 13:07:12 MST 2011
I have 2 identical boards, LPC1768 each using CAN1.  I have some test code based on the CAN led demo.  The processors are running at 100Mhz and the CAN bus is at 100K.

I set up the transmit for DLC=1, 2, 3, 4 ... 8 with data values of
data 1= 0x11
data 2= 0x22
data 7= 0x77
data 8=0x88

so I can quickly identify the bytes sent and received.

The problem:  If I set the xmit DLC to 1 through 7 all is OK in the received messages.   But if I set the xmit DLC to 8 I get byte 7 sent again in the byte 8 slot and the receive frame (RFS) register says the DLC is 7.  I get no errors.  I have put a CAN bus analyzer on the bus and the analyzer sees the correct frame with a dlc of 8 and 0x88 in the 8th byte so I know the transmit side is working OK.  It is something in the receive side.

I find it hard to belive that something as fundamental as DLC = 8 would not be working so I'm looking for any pointers to configuration isssues or other things I might look for to help figure this out.

I am only using CAN1 and CAN 2 is not powered up but I tried powering up CAN2 with the same results.  I cannot test CAN2 as those pins are in use for other functions.