CANbus

[Timmoore]

Hi Ingo,

Well spotted on the major bug . I dont know how many times I checked that - obviously not looking properly - either I was misled by the bogus bus activity which convinced me the output pin was correctly configured , and / or was counting the bits from 1 rather than zero - whatever the reason - a rookie error.

SO, it is all working beautifully now ! I have eight bytes being sent and received, I have tested the code running on 2 x 18F248, 1 x 18F248 and 1 x 18F4580 and finally 2 x 18F4580. All running nicely.

Glad my understanding of the workings of the registers is validated but have a red face for not checking the TRISB setting.

Thanks Ingo - I would rather have a red face AND working code than the other way around.

CANCON.3=1, you are probably correct, this may not be necesary for the simple test program. see page 276 of the 4580 datsheet. bits 3,2 and 1 are called WIN bits, which set the particular transmit or receive buffer . Code 100 sets tx buffer0. I suspect I may have to set these bits depending on the tx buffer I wish to use, equally on the rx side I can use these to place data in a particular rx buffer. I think there may be a degree of automation to this process but have yet to play with the system to fully understand the workings.

Now I must stop calling it the CANT bus and give its real name CAN bus !

Got some work to do now, adding data transfer functionality and structuring code.



Thanks again - Once done, I will send you a copy of my working system if you PM me or provide an e mail address.

[zx81sp]

I've post in PBP pro but nobody seems to know, so let me post here since is a CanBus question:

I've a small proto board (without datasheet) connected to a Can network and I'm trying to make a very simple app but I don't know how to do. It has a 18F258 (20Mhz clock) and MC2551 and I want just send a CAN command, nothing else. I know that the bus works at 100k, can anybody help me? just a help to start, I'm using now a CanUSB adapter with a PC but I want to use something lighter.

I've read the code above but sincerily, I don't understand it.

Regards

[inse]

CAN my be a little confusing in the beginning, but I am sure you will work into this.
PIC BASIC will not help you much regarding CAN communication, you will have to set all registers by hand.
As preparation you should do the following things:

1. check if your CAN transceiver has an enable pin and check its status
2. get the baudrate generator calculator from Microchip to calculate BRGCON register settings

Then you can prepare your code
3. configure you CANTX and CANRX pins correctly
4. set CANCON register to 128 for config mode
5. configure the BRGCON1..3 with the calculated values
6. configure the identifier registers TXB0SIDH and TXB0SIDL to generate the required message ID
7. configure the data length register TXB0DLC to match the length of your CAN message
8. configure the CIOCON register (usually CAN recessive high, bit 4 set)
9. set CANCON to 0 for normal mode
10. copy your CAN data to TXB0D0...TXB0D7
11. set the TXB0CON register to 8 to send your CAN message

.. and off you go!

[zx81sp]

CAN my be a little confusing in the beginning, but I am sure you will work into this....

Thank for your step-by-step guide! I'll try to begin with the project this weekend.

Regards

[zx81sp]

Well, I've connected the board to a PC using a CANUSB adapter listening at 100Kbps, but does not receive anything. This is the code (18F258+MCP2510 20Mhz):

define OSC 20

TRISB = %000001000 'portb.2 output, portb.3 input
CANCON = $80 'configuration mode 
'Set Data Rate based on 20Mhz to get 100 kbs:
BRGCON1 = $04 
BRGCON2 = $BF 
BRGCON3 = $02 

CIOCON = $10
TXB0SIDH = $0 
TXB0SIDL = $1 
CANCON = $0 'normal mode 

'
' Program
'
Main: 
        TXB0DLC = 8 
        TXB0D0 = 65
        TXB0D1 = 66
        TXB0D2 = 67
        TXB0D3 = 68
        TXB0D4 = 69
        TXB0D5 = 70
        TXB0D6 = 71
        TXB0D7 = 72
        TXB0CON = 8
    pause 1000
Goto main
End

What's wrong?

[inse]

Your program looks OK at first glance altough I didn't verify the BRG values.
What puzzles me is: do you really use an PIC18F258 in combination with an MCP2510?
Or do you use the PIC18F258 with the MCP2551 CAN transceiver as mentioned earlier?
The MCP2551 has a standby pin - how is it controlled?
It must be tied low for operation!
Check this and we can do further examination on the code.
Are you sure you have set up and connected your CAN-USB adaptor correctly?
A scope could show you if there is any activity on the bus.

[zx81sp]

Your program looks OK at first glance altough I didn't verify the BRG values.

I've got the BRG values using Microchip Can Bit Timing Calculator (from www.intrepidcs.com), it claims to be compatible with MCP2510, I think that the values are same for my MCP2551, also tried with the default values that the calculator shows (03/BF/07) but anyway nothing changes.

What puzzles me is: do you really use an PIC18F258 in combination with an MCP2510?
Or do you use the PIC18F258 with the MCP2551 CAN transceiver as mentioned earlier?

Sorry, the right combo is 18F258+MCP2551.

The MCP2551 has a standby pin - how is it controlled?
It must be tied low for operation!

RS Pin is connected to GND

Check this and we can do further examination on the code.
Are you sure you have set up and connected your CAN-USB adaptor correctly?

When I connect the CANUSB to the CAN network I can see the traffic, so I think that the problem it's not there. When I connect the adapter directly to the board I can't see activity, if the PBP code is right I must receive a command every second.

Thanks for your help!