Interfacing CANSPI with problems

Question

I am running a PIC18F with an HS oscillator of 40 MHz. The hardware is not the problem and all the connections are properly done. The microcontroller is connected to the MCP2510 (with a parallel cut crystal of 20 MHz) via SPI, so I can interact with the CAN bus line through the MCP2551. I have done the configuration to run at 1 Mbit/s, but it is not working because it is running at 500 kbit/s. The CAN bus configuration is correctly done, but it is not running as fast via SPI as I want.

Configuration:

• SJW=1
• BRP=1
• PSHEG1=7
• PSHEG2=5
• PROPSEG=7

The initialization of the SPICAN bus is done as the MikroElektronika CANSPI library.

I have been working on this a lot of time, and I think that the SPI initialization is the problem. As far as I know a 20 MHz crystal is enough to run the MCP2510 at 1 Mbit/s. Where is the problem? Is the SPI module running slower than I want?

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I do not know why, but when I change the speed it always divide it by two.

Answer 1

When troubleshooting serial buses, an oscilloscope is invaluable. If you don't have a lab grade instrument, pick up a simple, inexpensive USB scope. There are also inexpensive CAN/SPI diagnostic modules available in USB format.

It is always a good practice when troubleshooting serial bus problems, to significantly reduce the bus speed. This not only makes it easier to spot problems with a scope, but the effect of parasitics is dramatically reduced. Once you getting it working at low speed, you can raise the frequency to observe and isolate any changes.