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Transmission errors of CAN

 
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minttujatapsa



Joined: 19 Oct 2004
Posts: 2

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Transmission errors of CAN
PostPosted: Fri May 06, 2005 5:15 am     Reply with quote
Hi,

Does anyone know how PICs handle the situation in where those cannot transmit data successfully. If I understood right it just gives up, and doesn't try resend automatically. Am I right?

If it do so, is there any way to force it to try transmitting until it will success?

Best regards

tr
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri May 06, 2005 5:07 pm     Reply with quote
There are a few places in Microchip CAN Controller data sheets
where they say that the chip will do automatic re-transmission
in case of an error.

Quote:

From the MCP2510 data sheet, page 16:
After transmission of a message has begun, if an error
occurs on the bus or if the message loses arbitration,
the message will be retransmitted regardless of
a request to abort.


Quote:

From the MCP2515 data sheet, page 15:
Normally, if a CAN message loses arbitration or is destroyed
by an error frame, the message is retransmitted.


I can't find any statements in the 18F458 data sheet or Reference
manual that state it as openly as above.
Quote:
From the 18F Reference manual, in section 22.5.2:
Note that the automatic retransmission of messages on the
bus line is handled by the FSM.


AN713 has more information:
Quote:
On page 4, in the Error Passive section, it says:
When an Error-Passive node transmits a Passive Error Flag
and detects a dominant bit, it must see the bus as being idle
for eight additional bit times after an intermission before
recognizing the bus as available. After this time, it will
attempt to retransmit.


Quote:
In AN713, in the Bus-Off section, on page 4:
There is a bus recovery sequence that is defined by the CAN
protocol that allows a node that is Bus-Off to recover, return
to Error-Active, and begin transmitting again if the fault
condition is removed.
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