| View previous topic :: View next topic |
| Author |
Message |
timk
Joined: 03 Aug 2018
Posts: 11
|
| PIC18F46K80 Can Interface |
 Posted: Wed Oct 16, 2019 7:31 am |
 |
|
Hello!
Currently I want to use the CAN Interface of the PIC18F46K80.
I am using the CCS Compiler with the CCS IDE.
The Help Section of the CCS IDE says, that I should be able to init the CAN-Bus with an "can_init(void);" command.
But If I want to compile, the compiler says "Undefined Identifier".
How can I use these CAN-functions?
Or is there any other driver I could use for Communicating over CAN?
Thanks in Advance! |
|
 |
temtronic
Joined: 01 Jul 2010
Posts: 9093
Location: Greensville,Ontario
|
|
| Posted: Wed Oct 16, 2019 7:43 am |
|
|
The best place to start would be using the CAN examples, from the EXAMPLES folder.
I don't use CAN (too much overhead), but I'd try the CCS examples. Be sure to read the embedded comments in the code !
Jay |
|
|
PCM programmer
Joined: 06 Sep 2003
Posts: 21708
|
| Re: PIC18F46K80 Can Interface |
| Posted: Wed Oct 16, 2019 9:44 am |
|
|
| timk wrote: | Hello!
The Help Section of the CCS IDE says, that I should be able to init the CAN-Bus with an "can_init(void);" command.
But If I want to compile, the compiler says "Undefined Identifier".
|
The CAN bus functions are not built-in to the compiler. You have to
#include a driver file. In the help file, it lists the CAN Bus driver files
that CCS has available:
| Quote: | Relevant Include Files:
can-mcp2510.c - Drivers for the MCP2510 and MCP2515 interface devices.
can-18xxx8.c - Drivers for the built-in CAN module.
can-18F4580.c - Drivers for the built-in ECAN module
|
Since you are using the 18F46K80, the best one for your PIC is shown
in bold above.
The only CCS example file that uses that driver file is this one:
Look in the CCS Examples directory on your PC to find this file. |
|
|
timk
Joined: 03 Aug 2018
Posts: 11
|
|
| Posted: Wed Oct 16, 2019 11:53 pm |
|
|
Okay, thank you.
I think I can work with that.
Haven't seen these examples before. |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19215
|
|
| Posted: Thu Oct 17, 2019 2:16 am |
|
|
We need a big red headline on the forum. Something like:
The CCS examples, are one of the main things you should always look at....
 |
|
|
temtronic
Joined: 01 Jul 2010
Posts: 9093
Location: Greensville,Ontario
|
|
| Posted: Thu Oct 17, 2019 4:33 am |
|
|
I agree with Mr. T !
Actually the examples were one reason I bought PCM over 2 decades ago. Since I had/have ZERO C formal programming, they allowed me to see how to cut code. While my programs do not conform to official C standards for layout and such, they function. CCS even sent me an updated version of the Examples library and while some programs I can't use, they show HOW to access PIC features. |
|
|
fkl
Joined: 20 Nov 2010
Posts: 44
|
|
| Posted: Tue May 02, 2023 6:17 am |
|
|
hello.
PIC18F46K80
As an example, do I need to use ex_can_ccs_a.c ?
How to calculate these variables correctly in relation to 500K bus speed?
| Code: |
#define CAN_BRG_PRESCALAR 3 //Set CAN Baud Rate to 125K
#define CAN_BRG_PHASE_SEGMENT_1 6 //Tq = (2*(1+PRESCALAR))/Fosc
#define CAN_BRG_PHASE_SEGMENT_2 6 //Tq = (2*(1+3))/16000000 = 0.0000005
#define CAN_BRG_PROPAGATION_TIME 0 //Baud Rate = 1/(((PHASE_SEGMENT_1+1)+(PHASE_SEGMENT_2+1)+(PROPAGATION_TIME+1)+1)*Tq)
#define CAN_BRG_SYNCH_JUMP_WIDTH 0 //Baud Rate = 1/(((6+1)+(6+1)+(0+1)+1)*0.0000005) = 125000
|
What processor clock frequency is needed for 500K bus speed, 16MHz (#use delay(internal=16000000)) - will it be sufficient or do I need to increase the frequency to 64MHz and use an external clock crystal? |
|
|
temtronic
Joined: 01 Jul 2010
Posts: 9093
Location: Greensville,Ontario
|
|
| Posted: Tue May 02, 2023 6:58 am |
|
|
the equations you need to use are in the comments !
How you calculate is up to you..
1) cut a program using them....
2) create a spreadsheet using them
or
3) grab a pencil and pad and use them.....
another option is to have the CAN program automatically figure all this out based upon desired baud rate and clock value. |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19215
|
|
| Posted: Tue May 02, 2023 7:02 am |
|
|
Use one of the online calculators.
The formulae are there in the MicroChip data sheet, and application notes,
but the calculators are easier.
[url]
https://www.medo64.com/2014/05/canbus-setup/
[/url]
MicroChip have their own one, but this is simpler to use.
You can do 500K at 16MHz OK.
'Internal' is potentially slightly problematical, since it can easily take you
outside the allowed tolerance. Just like USB, where the clock accuracy
required is higher than the accuracy of most internal oscillators, CAN is
quite strict on it's timings. It normally requires a master oscillator that
is better than 0.5% accurate. The internal oscillator only manages +/-2%.
[url]
https://www.analog.com/en/design-notes/design-considerations-for-can-bus-and-asynchronous-serial.html
[/url]
So you don't 'need' to increase to 64MHz. Will depend on what you actually
want the processor to do. But you do really need a crystal or ceramic
resonator. |
|
|
fkl
Joined: 20 Nov 2010
Posts: 44
|
|
| Posted: Tue May 02, 2023 7:34 am |
|
|
| Code: |
//setup pins
TRISB2 = 0;
TRISB3 = 1;
CANCON = 0b10000000; //set to Configuration mode
while ((CANSTAT & 0b11100000) != 0b10000000);
BRGCON2bits.SEG2PHTS = 1; //freely programmable SEG2PH
BRGCON1bits.BRP = 0;
BRGCON2bits.PRSEG = 6; //7 Tq
BRGCON2bits.SEG1PH = 5; //6 Tq
BRGCON3bits.SEG2PH = 1; //2 Tq
BRGCON1bits.SJW = 1; //2 Tq
ECANCONbits.MDSEL = 2; //Enhanced FIFO mode
CANCON = 0b00000000; //set to Normal mode
while ((CANSTAT & 0b11100000) != 0b00000000);
|
please tell me how to assign correctly calculated values (variable names are different in the calculator, it is for another language), if it doesn’t make it difficult |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19215
|
|
| Posted: Tue May 02, 2023 7:48 am |
|
|
| Just read the data sheet. The names are self explanatory. |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19215
|
|
| Posted: Tue May 02, 2023 9:17 am |
|
|
BRP Baud Rate Prescaler
SEG1PH Segment 1 phase
SEG2PH Segment 2 phase
SJW Synchronization jump width
PRSEG Propagation time
If you look at the CCS names, the relationship is obvious. |
|
|
fkl
Joined: 20 Nov 2010
Posts: 44
|
|
| Posted: Tue May 02, 2023 10:31 am |
|
|
| Code: |
#define CAN_BRG_PRESCALAR 0
#define CAN_BRG_PHASE_SEGMENT_1 5
#define CAN_BRG_PHASE_SEGMENT_2 1
#define CAN_BRG_PROPAGATION_TIME 6
#define CAN_BRG_SYNCH_JUMP_WIDTH 1
//Set CAN Baud Rate to 500K
//Fosc=16MHz
|
correct? |
|
|
fkl
Joined: 20 Nov 2010
Posts: 44
|
|
| Posted: Thu May 11, 2023 6:26 am |
|
|
In the help ccs c only lists the functions of the CAN bus, in general there is a more detailed description of these functions?
In particular, how to add filters and masks correctly? |
|
|
Ttelmah
Joined: 11 Mar 2010
Posts: 19215
|
|
| Posted: Fri May 12, 2023 2:12 am |
|
|
Two things here.
First you need to read up on CAN itself.
Second get the Microchip application note 70070D.
The acceptance filters and filter masks are part of the CAN specification.
How these are implemented on the PIC, the application note covers. |
|
|
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
