This is the mail archive of the mailing list for the eCos project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

CAN bus on olimex LPC-L2294

I have hard time to make CAN working on OLIMEX LPC-L2294. Both
transmitting and receiving doesn't work for me. I have two LPC-L2294
boards wired by CAN cable made by me. I double verified that it is
wired correctly.  Receiving didn't work, so I concentrated on
transmitting and measured signal between driver and LPC with
oscilloscope. The transmitting program is derived from test
ecos/packages/devs/can/arm/lpc2xxx/current/tests/can_rx_tx.c . The
application got stuck on 33rd message after sending 32 messages. Yes -
the transmitting queue is configured to have length 32. The LPC is
transmitting indefinitely the same pattern which will be described
later. My thought was that CAN controller doesn't have a feedback for
arbitration, so RD1 is not connected properly. I verified that signal
is physically on RD1 by oscilloscope and that PINSEL1 was not
overwritten by some other module.

The first message (which I believe is transmitted indefinitely) ID is
0 and I use standard message (11bit identifier). The data length is 0.
The CAN BUS speed is 100kbits, so 1bit width is 10 [usec]. I am not
sure if this behavior is correct because message was not acknowledged
by any node, but I tried to receive data be other board with no

I see the following pattern repeatly

d = dominant (L),  r = recessive(H),   5d = 5 dominant bits


all 1r in pattern is bit stuffing

I am not sure where is the Start-of-frame in this pattern to analyze
it more precisely. But it seems that it transmitted 34 bits (5d*6+4d),
which is can be data from Start-of-frame to CRC. But why block 27r
doesn't contain stuffing bits? Is ACK by any node in CAN mandatory?

I appreciate any input or thought.
Bronislav Gabrhelik

Before posting, please read the FAQ:
and search the list archive:

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]