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DsPIC Block/CAN Configuration

From http://www.kerhuel.eu/wiki - Simulink device driver Blockset for dsPIC / PIC24 / PIC32 Microcontrollers --[[User:LubinKerhuel|LubinKerhuel]] 12:40, 3 September 2009 (UTC)
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Block CAN Configuration

Configuration for the CAN Peripheral

When using either a CAN Receive block or a CAN Transmit block, this block configure the mode and the CAN BUS parameters.

Dialog Box Parameters

CAN Configuration Dialog

Num CAN

Ref to the CAN peripheral being configured (some PICs have two CAN buses)

Mode

Configure the mode of the CAN peripheral. Four options are available.

  • Normal : the one you will use in most cases.
  • Loop back : Allows testing of the CAN peripheral and the CAN blockset. In this mode, no external connection or driver is necessary to make the CAN peripheral work. Messages transmitted are routed directly into the receive logic.
  • Listen only : The CAN peripheral receives messages on the bus without transmitting (not even acknowledge bits).

This mode will use only the Receive pin of the CAN peripheral The Transmit pin can be used for another purpose.

  • Disable : shut down the CAN peripheral.

These parameters configure the Timing of the CAN bus. Refer to the CAN documentation for more information.

The existing parameter prompts are poor: I have suggested new ones here (the block-set still looks as shown).

  • TRefCAN
  • Baud Rate Prescaler - 1
  • Propagation Time Segment quanta
  • Phase Buffer Segment 1
  • Times to Sample
  • Phase Buffer Segment 2
  • Synchronisation max jump (Tq)

The time quanta Tq and the bus frequency Fcan are updated in the Info display each time one of these parameters is modified.

Sample Time

Sample time of the block. -1 for inherited

Block Ordering Input / Output

If you want to force the execution order of blocks that are not connected, this option allow to add either an input, an output or both to the block. These virtual connection allow to force the ordering of the blocks.

Info

Information: the time quantum length Tq and the baud rate of the CAN, given the input oscillator timing TRefCan

Warning

The baud rate is currently incorrectly given for at least the pic30f6014A. It corresponds to 1 more quantum than is actually given to each bit. Reduce one of the segment lengths by 1 quantum temporarily to see the correct baud rate.

In addition, the smallest bit length should be 8 quanta, but the block allows fewer than this to be configured (and shown in the Info display).

I suspect this affects many, if not all, PIC microcontrollers with CAN (rather than ECAN) modules.

see forum related remark: http://www.kerhuel.eu/forum/viewtopic.php?f=8&t=387

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