Interface NXP SJA1000 CAN Controller to Freescale iMX

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- bung89
  
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posted
16 years ago

Tue, Jan 29, 2008 11:56 AM

Hi Folks,

I'm working on a project based around the Freescale iMX.31 microcontroller requiring a CANopen interface. I therefore need a CAN2.0B (Active) compatible stand-alone controller.

We plan to test the CAN bus with the IXXAT USB-CAN interface which incorporates the NXP SJA1000. This and the fact that the SJA1000 appears to be a very popular controller, makes it my top choice.

The SJA1000 has a multiplexed address/data bus and the iMX.31 has seperate address and data buses. I will have to multiplex the lower byte of the iMX.31 address and data buses using some logic such as an octal bus switch or mux/demux, and also consider the control signals and timing etc.

My question is - Can anyone offer any advice on the best way to do this?

Much appreciated, Al

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- MK
  
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posted
16 years ago

Wed, Jan 30, 2008 8:56 AM

Don't do it.

Unless there is a compelling reason to have a nasty noisy parallel bus with extra chips to multiplex signals.

There are very few stand alone CAN controller chips but you should look at the Microchip MCP2515 which has an SPI interface to the processor.

Alternatively use a micro with built in CAN and then SPI (or I2C or UART) that to your main processor.

Michael Kellett

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- bung89
  
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posted
16 years ago

Fri, Feb 1, 2008 12:08 PM

Using a micro with a CAN controller built-in would mean writing more software for another micro, as well as the fact that each device would have to be programmed in production - not an ideal use of time if it can be avoided.

I did consider other CAN controllers including the MCP2515 but would prefer a parallel interface for greater throughput if required. The OKI ML9620 is going obsolete soon, so that's a no no for new designs.

The iMX I/O operates at 1.8V, I'm having to use transceivers on the address and data buses to interface with a 3.3V Ethernet controller, I'm not worried about noise as I've used this multi-supply arrangement before and observed no significant noise on a scope.

Another way I am considering the interface is to just use the data bus and make two accesses to the SJA1000, the first for the address and the second for the data.