Lpc2000

I am trying to write some functions that will test if the CAN
controller is working properly.  I've figure out how to use CANMOD-STM
and CANCMR-SRR together to form an internal loopback.  What is
CANMOD-TM for?  Everytime I use it, I get an error.

I emailed this question to philips and this was their complete response:

"I'm not 100% certain but I beleive you need to connect the transmit
pin to the receive pin externally."

Not very helpful.

--Peter


--- In lpc2000@yahoogroups.com, "peterburdine" <lordofdawn@h...> wrote:

> 
> I am trying to write some functions that will test if the CAN
> controller is working properly.  I've figure out how to use CANMOD-STM
> and CANCMR-SRR together to form an internal loopback.  What is
> CANMOD-TM for?  Everytime I use it, I get an error.

That's pretty useless advice.

The documentation states that the TM cause the state of the RX pin to be 
copied to the TX pin. 

To me this sounds like an "external loop-back" that you can use to cause the 
received data to be looped back to the outside world without going through 
the CAN controller. I guess this *could* be used for some things, but if you 
have a standard 82C250/251-style CAN transeiver this will do nothing useful 
since it will just cause the transceiver to latch up.

If the above is true, then I am not suprised that the CAN controller goes 
silly when you invoke this mode.

For product level testing, what I do is hook the CAN lines to another device 
in the test harness that has been configured for the same bit-rate: If the 
device under test (DUT) can siuccessfully transmit a frame, then I know the 
following happened:
i. DUT send data.
ii. Test harness sees the frame and sends Ack bit.
iii. DUT sees Ack bit.
Thus the whole rx/tx circuitry has been tested successfully.

On Wednesday 30 March 2005 09:31, peterburdine wrote:
> I emailed this question to philips and this was their complete response:
>
> "I'm not 100% certain but I beleive you need to connect the transmit
> pin to the receive pin externally."
>
> Not very helpful.
>
> --Peter
>
> --- In lpc2000@yahoogroups.com, "peterburdine" <lordofdawn@h...> wrote:
> > I am trying to write some functions that will test if the CAN
> > controller is working properly.  I've figure out how to use CANMOD-STM
> > and CANCMR-SRR together to form an internal loopback.  What is
> > CANMOD-TM for?  Everytime I use it, I get an error.
>
> Yahoo! Groups Links
>
>
>