Component: CAN (Internal, MCP2515) (Comms: Interface)

Author	Matrix Ltd
Version	2.10
Category	Comms: Interface

CAN (Internal, MCP2515) component

Low level routines for controling the CAN interface either using an external MCP2515 IC and a SPI bus connection or using an internal CAN peripheral if available on your device. Both methods will require a CAN driver IC like the MCP2551 to drive the CAN signals on the bus.

Component Pack

COMMSA

Detailed description

No detailed description exists yet for this component

Examples

Internal CAN schematic

External CAN schematic

CAN Message Decoding

The CAN component works together with the injector component to allow you to decode a CAN message ID into a meaningful command.

Example File CAN_Example1 When a key on the keypad is pressed the CAN components transmits a CAN packet.

The CAN packet is decoded by the injector component to give us a meaningful log on the console window.

High Level CAN Data Console

Low Level CAN Data Console

Reference from CAN Injector to ID decode file, $(srcdir) refers to the current project directory.

Demo CAN ID file File:CANID.csv

CAN Masks and Filters

How to work out which messages will be trapped by a particular mask/filter combination

Note that all values for message id's, masks and filters are numbers between 0x000 and 0x7FF.

Example 1

Mask0 = 0x0FF

Filter0 = 0x100

Filter1 = 0x050

In binary, this looks like:

Mask0 = 000 1111 1111

Filter0 = 001 0000 0000

Filter1 = 000 0101 0000

For the mask, a "1" signifies "check this bit" and a "0" means "ignore this bit"

So, these filters will accept the following messages ("x" = don't care)

Filter0 = xxx 0000 0000

Filter1 = xxx 0101 0000

i.e.

Filter0 = 0x000, 0x100, 0x200, 0x300, 0x400, 0x500, 0x600, 0x700

Filter1 = 0x050, 0x150, 0x250, 0x350, 0x450, 0x550, 0x650, 0x750

Example 2

Mask1 = 0x350

Filter2 = 0x200

Filter3 = 0x123

Filter4 = 0x3FF

Rewriting in binary:

Mask1 = 111 0101 0000

Filter2 = 010 0000 0000

Filter3 = 001 0010 0011

Filter4 = 111 1111 1111

Here, the mask will only check 4 bits and ignore the other 6. Here's what the filters will accept:

Filter2 = 010 x0x0 xxxx

Filter3 = 001 x0x0 xxxx

Filter4 = 111 x1x1 xxxx

They will actually trap a lot of messages (64 each!):

Filter2 = 0x200, 0x201, 0x202, ... 0x220, 0x221, ... 0x280, 0x281, ... 0x2A0, 0x2A1, ... 0x2AF

Filter3 = 0x100, 0x101, 0x102, ... 0x120, 0x121, ... 0x180, 0x181, ... 0x1A0, 0x1A1, ... 0x1AF

Filter4 = 0x750, 0x751, 0x752, ... 0x770, 0x771, ... 0x7D0, 0x7D1, ... 0x7F0, 0x7F1, ... 0x7FF

This second example is not very practical. In general, it is more logical to set the mask so that each filter accepts a consecutive range of messages.

As you can see, the mask determines which bits of the filters are actually looked at. Setting the mask to 0x000 will effectively mean that the filter will accept any incoming message. Also, the value of the mask directly relates to how many messages each filter will trap - i.e. 2^(number of '0' bits in the mask).

A useful way to use the mask would be to ignore the least significant bits. Lets say that you wanted the filters to accept 16 messages each - setting the Mask0 to 0x7F0 would achieve this. Then, setting the filters to the following:

Filter0 = 0x100

Filter1 = 0x110

would mean that the following messages are accepted:

Filter0 = 0x100, 0x101, 0x102, 0x103, 0x104, ... 0x10D, 0x10E, 0x10F

Filter1 = 0x110, 0x111, 0x112, 0x113, 0x114, ... 0x11D, 0x11E, 0x11F

Of course, for simple CAN applications you may wish to only accept one or two messages. Setting the mask to 0x7FF in this instance would mean that only the message ID specified by each filter would be accepted, e.g.

Mask1 = 0x7FF

Filter2 = 0x100

Filter5 = 0x200

This would mean that only messages 0x100 and 0x200 would be accepted into buffer 1.

Downloadable macro reference

	ReadSwitches
Returns switch input states from the external MCP2515 device. 0 = No Switch Pressed, 1 = Switch 1 Pressed, 2 = Switch 2 Pressed, 3 = Both Pressed (External CAN only)
- BYTE	Return

	SetTxData
Assigns one of the outgoing transmit buffers with data ready to be sent.
- BYTE	Buffer
- BYTE	Count
- BYTE	d0
- BYTE	d1
- BYTE	d2
- BYTE	d3
- BYTE	d4
- BYTE	d5
- BYTE	d6
- BYTE	d7
- VOID	Return

	SetRxMask
Allows the receive ID mask to be configured on the fly allowing different ID ranges to be received.
- BYTE	Mask
Specifies which receive mask to modify. Range: 0-1
- ULONG	ID
The ID mask value you wish to use
- VOID	Return

	GetRxData
Returns last received message data byte at position Index. Buffer parameter is currently ignored
- BYTE	Buffer
- BYTE	Index
- BYTE	Return

	GetRxIDHi
Gets the Hi byte Rx ID in register format. Standard ID only 0-2047. Compatible with v5 component and previous,
- BYTE	Buffer
Receive Buffer. Range 0-1
- BYTE	Return

	SetTxIDSimple
Set the Tx CAN ID as a generic number. Standard IDs only 0-2047.
- BYTE	Buffer
Transmit buffer to load. Range: 0-2
- UINT	ID
The ID value you wish to use. Range: 0-2047
- VOID	Return

	SendBuffer
Transmits one of the transmit buffers which should have already been populated with an ID and data.
- BYTE	Buffer
Specifies which transmit buffer to send
- VOID	Return

	GetRxDataCount
Returns last received message data length. Buffer parameter is currently ignored
- BYTE	Buffer
- BYTE	Return

	SetRxFilterID
sets the Filter Standard mode only (for V5 compatibility only)
- BYTE	Filter
Specifies which filter to modify. Range: 0-5
- BYTE	Hi
ID bits 3-10
- BYTE	Lo
ID bits 0-2 stored in the upper 3 bits of the byte
- VOID	Return

	GetRxIDLo
Gets the Lo byte Rx ID in register format. Standard ID only 0-2047. Compatible with v5 component and previous,
- BYTE	Buffer
- BYTE	Return

	SetRxMaskID
set the Mask Standard ID mode only (for V5 compatibility)
- BYTE	Mask
Specifies which receive mask to modify. Range: 0-1
- BYTE	Hi
ID bits 3-10
- BYTE	Lo
ID bits 0-2 stored in the upper 3 bits of the byte
- VOID	Return

	SetRxFilter
Allows the receive ID filter to be configured on the fly allowing different ID ranges to be received.
- BYTE	Filter
Specifies which receive filter to modify. Range: 0-5
- ULONG	ID
The ID filter value you wish to use
- VOID	Return

	SetTxIdent
Set the Tx CAN ID as a generic number. Standard and extended IDs Standard 0-2047 Extended 2048-536870911
- BYTE	Buffer
Transmit buffer to load. Range: 0-2
- ULONG	ID
The ID or Extended ID value you wish to use. Range: 0-536870911
- VOID	Return

	CheckRx
Checks to see if any messages are available for 'Buffer' specified
- BYTE	Buffer
Send buffer: 0 to 1
- BYTE	Return

	ChangeRate
Simple attempt to alter the bus rate of the CAN. External CAN channels only,
- BYTE	Rate
Rate: 0-3 where 0=125, 1=250, 2=500, 3=1000
- VOID	Return

	GetRxIDSimple
Gets the Rx ID as a Integer Standard ID only 0-2047.
- BYTE	Buffer
Receive Buffer. Range 0-1
- UINT	Return

	SetTxID
Set the Tx CAN ID in register format. Standard ID only 0-2047. Compatible with v5 component and previous,
- BYTE	Buffer
Transmit buffer to load. Range: 0-2
- BYTE	Hi
ID bits 3-10 e.g. ((ID & 0x7F8) >> 3)
- BYTE	Lo
ID bits 0-2 stored in the upper 3 bits of the byte e.g. ((ID & 0x7) << 5)
- VOID	Return

	ShowLEDs
Set LED state (External CAN only)
- BYTE	led1
Controls LED 1. Range: 0-1
- BYTE	led2
Controls LED 2. Range: 0-1
- VOID	Return

	GetRxIdent
Gets the Rx ID as a Integer Standard and Extended IDs.
- BYTE	Buffer
- ULONG	Return

	Initialise
Must be called before any other CAN component macros to enable and initialise the CAN peripheral.
- VOID	Return

Property reference

	Properties
	Channel
Switches between Internal CAN peripheral and External CAN controller IC MCP2515.
	Controller Osc
	Bus Rate
Data rate of the bus specified in thousand bits per second, Kbps.
	Sync Jump Width
Defines how far a resyncronisation may move the sample point
	Sample Point
Point in each bit period where the incoming data is sampled.
	ID Type
Switches between using Standard, or Standard and Extended CAN
	One Shot Mode
Disabled. Messages will reattempt transmission Enabled. Message will only attempt to transmit once
	Connections
	SPI
	CHANNEL
SPI Channel selector
	MOSI
SPI Data Out Pin SDO - Also Known as Master Out Slave In (MOSI) when used in Master mode.
	MISO
SPI Data In Pin SDI - Also Known as Master In Slave Out (MISO) when used in Master mode.
	CLK
SPI Clock Pin CLK - The Clock signal is driven by the SPI master.
	SS
Chip Select / Slave Select Pin Master Mode: General purpose output pin used to select the remote SPI device. Slave Mode: Hardware chip select pin input used to select the SPI device.
	Prescale
Prescale option selector
	Sample Point
Data bit read sample point
	Config Delay
	TX Buffer 0
	Message ID
TX Buffer 0 Message Identifier
	Length
TX Buffer 0 Number of data bytes
	D0
TX Buffer 0 Data Byte 0
	D1
TX Buffer 0 Data Byte 1
	D2
TX Buffer 0 Data Byte 2
	D3
TX Buffer 0 Data Byte 3
	D4
TX Buffer 0 Data Byte 4
	D5
TX Buffer 0 Data Byte 5
	D6
TX Buffer 0 Data Byte 6
	D7
TX Buffer 0 Data Byte 7
	TX Buffer 1
	Message ID
TX Buffer 1 Message Identifier
	Length
TX Buffer 1 Number of data bytes
	D0
TX Buffer 1 Data Byte 0
	D1
TX Buffer 1 Data Byte 1
	D2
TX Buffer 1 Data Byte 2
	D3
TX Buffer 1 Data Byte 3
	D4
TX Buffer 1 Data Byte 4
	D5
TX Buffer 1 Data Byte 5
	D6
TX Buffer 1 Data Byte 6
	D7
TX Buffer 1 Data Byte 7
	TX Buffer 2
	Message ID
TX Buffer 2 Message Identifier
	Length
TX Buffer 2 Number of data bytes
	D0
TX Buffer 2 Data Byte 0
	D1
TX Buffer 2 Data Byte 1
	D2
TX Buffer 2 Data Byte 2
	D3
TX Buffer 2 Data Byte 3
	D4
TX Buffer 2 Data Byte 4
	D5
TX Buffer 2 Data Byte 5
	D6
TX Buffer 2 Data Byte 6
	D7
TX Buffer 2 Data Byte 7
	RX Buffer 0
	Settings
RX Buffer 0 Message Receive Mode
	RX Buffer 1
	Settings
RX Buffer 1 Message Receive Mode
	Simulation
	Label
Comms Flasher Identification Label
	Simulate SPI Comms