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Message |
stoyanoff
Joined: 20 Jul 2011
Posts: 375
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| CAN bus transmission problem |
 Posted: Tue Aug 12, 2014 2:03 am |
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Greetings! I'm using 2 PIC18F2550 with MCP2515 and MCP2551. I have MPLab v8.91 and CCS v4.134.
Here are my programs:
SPI:
| Code: |
#define EXT_CAN_CS PIN_B4
#define EXT_CAN_SI PIN_B0
#define EXT_CAN_SO PIN_C7
#define EXT_CAN_SCK PIN_B1
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Transmitter:
| Code: |
#include <18F2550.h>
#FUSES HS,NOWDT,CPUDIV1
#use delay(clock=10M)
#include <can-mcp2515.c>
int status;
void main()
{
int32 tx_id=24;
int tx_pri=3;
int1 tx_ext=0;
int1 tx_rtr=1;
output_high(PIN_B5);
delay_ms(100);
can_init();
while(1)
{
if(can_tbe())
{
status=can_putd(tx_id,5,1,tx_pri,tx_ext,tx_rtr);
}
delay_ms(10);
}
}
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Receiver:
| Code: |
#include <18F2550.h>
#FUSES HS,NOWDT,CPUDIV1
#use delay(clock=10M)
#include <can-mcp2515.c>
int dataHolder[10];
void main()
{
int32 rx_id;
int rx_len;
struct rx_stat rxstat;
output_high(PIN_B5);
delay_ms(100);
can_init();
while(1)
{
if(can_kbhit())
{
if(can_getd(rx_id,&dataHolder[0],rx_len,rxstat))
{
delay_ms(1);
}
}
}
}
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I don`t receive anything on the receiver. I even don't pass the can_kbhit().
Is there any problem with my programs?!
Thanks! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Aug 12, 2014 6:19 pm |
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This thread has a link to a 2-board CAN bus test program.
http://www.ccsinfo.com/forum/viewtopic.php?t=39809
There is also sample code for a loopback test for mcp2515.
It's helpful to test the mcp2515 in loopback mode first, so you can prove
that your SPI communication is working correctly. Then do the 2-board
test to prove that two CAN bus boards can talk to each other. |
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stoyanoff
Joined: 20 Jul 2011
Posts: 375
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| Posted: Sat Aug 16, 2014 11:34 pm |
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OK! I ran the loop back test and it`s OK, but it doesn`t transmit on line.
Here you can see my schematic
I have pull up resistors on SPI pins, too. Reset pin is high!
Are there any errors?!
Thanks! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Aug 17, 2014 12:32 am |
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| Quote: | | but it doesn`t transmit on line. |
How are you testing this ? Are you using your programs that you posted
earlier in this thread ? Or are you using my 2-board test program here:
http://www.ccsinfo.com/forum/viewtopic.php?t=29627&start=7
Also, on your schematic, you have the SDO and SDI pins swapped.
But it doesn't matter because the mcp-251x.c driver uses software SPI
by default. In earlier compiler versions, it only use software SPI.
So you're OK with those connections. It just wouldn't work with
hardware SPI. You don't need to change it right now. |
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alan
Joined: 12 Nov 2012
Posts: 357
Location: South Africa
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| Posted: Sun Aug 17, 2014 12:32 am |
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I have not read your datasheet, but normally SI would go to SO on a slave master config. What normally helps me i to define the pins as MOSI for master or MISO for the slave.
Regards |
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stoyanoff
Joined: 20 Jul 2011
Posts: 375
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| Posted: Sun Aug 17, 2014 6:15 am |
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| If this is true, why I have response in the loop back test?! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Aug 17, 2014 10:52 am |
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Stoyanoff,
I told you in my earlier post:
| Quote: |
Also, on your schematic, you have the SDO and SDI pins swapped.
But it doesn't matter because the mcp-251x.c driver uses software SPI
by default. In earlier compiler versions, it only use software SPI.
So you're OK with those connections. It just wouldn't work with
hardware SPI. You don't need to change it right now |
.
And you didn't answer my question
| Quote: | How are you testing this ? Are you using your programs that you posted
earlier in this thread ? Or are you using my 2-board test program here: |
So I don't want to continue this. |
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stoyanoff
Joined: 20 Jul 2011
Posts: 375
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| Posted: Sun Aug 17, 2014 10:36 pm |
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| Sorry! My fault! I`m using the programs from the link you gave me. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Aug 18, 2014 1:08 am |
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OK, each MCP2515 must connected to a MCP2551 transceiver chip.
Then the two MCP2551 chips must be connected to each other.
It has to look similar to this schematic, except that instead of ATMega
chips, you have 18F2550 PICs:
http://www.bobandeileen.com/wp-content/uploads/2007/08/schematic.JPG
An RS232 cable must be connected between the 1st board and your PC.
| Code: | rs232 CAN
PC <-----> Board1 <---> Board2 |
| Quote: | | but it doesn`t transmit on line. |
If it doesn't transmit, then tell us how you know this. Are you looking
at CANH and CANL with an oscilloscope ? Tell us, in detail, how you
know it doesn't work. |
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stoyanoff
Joined: 20 Jul 2011
Posts: 375
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| Posted: Fri Aug 22, 2014 3:35 am |
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Thanks, a lot! I fixed it! I had a bad connection on the one MCP2551.
Just for the record connections are:
controller <-> MCP2515
SI - SI
SO - SO
as PCM programmer`s schematic!
I there any chance to use another source for MCP2515 oscillator. For example to use one of the PWM exits of PIC18F2550 or RC group?! |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19520
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| Posted: Fri Aug 22, 2014 3:42 am |
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The easiest thing, is to use an external oscillator module, at 8MHz, and run both the PIC, and the MCP from this. 
Best Wishes |
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