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pic_beginner
Joined: 07 Feb 2011
Posts: 2
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| pic18F2580 and CAN-bus |
 Posted: Mon Feb 07, 2011 11:57 am |
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I am trying to connect NOx sensor with my pic via can-bus,
(NOx sensor: 500kbaud, can-format motorola, identifier: standard.)
and I don't receive any messages from it.
loopback mode is ok.
| Code: |
#include <18F2580.h>
#fuses INTRC_IO,NOWDT,PROTECT,NOLVP,NODEBUG,EBTRB,NOMCLR
#use delay(clock=16000000)
#include <stdlib.h>
#include <mcp4921_3.c>
#include <mcp4921_4.c>
#include <can-18F4580.c>
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
#define OSC_16MHZ
#define OSC_INTRC
void main(void)
{ can_init();
can_set_mode(CAN_OP_CONFIG);
BRGCON1.brp = 1;
BRGCON1.sjw = 0;
BRGCON2.prseg = 0;
BRGCON2.seg1ph = 4;
BRGCON3.seg2ph = 2;
BRGCON2.sam=1;
BRGCON2.seg2phts=1;
BRGCON3.wakfil=0;
can_set_mode(CAN_OP_NORMAL);
while(TRUE)
{
if ( can_kbhit() ) //if data is waiting in buffer...
{
if(can_getd(ID,&buffer[0], rx_len, rxstat)) { //...then get data from buffer
br=7;
}
else {
br=1;
}
}
//every two seconds, send new data if transmit buffer is empty
if ( can_tbe() )
{
i=can_putd(0x120,&data1[0],8,1,1,0);
//put data on transmit buffer
if (i != 0xFF) { //success, a transmit buffer was open
bt=7;
}
else
{
bt=1;
}
delay_ms(200);
}
}
}
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collink
Joined: 08 Jan 2010
Posts: 137
Location: Michigan
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| Posted: Tue Feb 08, 2011 6:07 am |
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It would probably help if you set your baud rate to 500k instead of the 800k baud you are currently setting.
Here is how you currently have it:
16,000,000 hertz clock.
All set values are one higher than set so you have a prescale of 2. That's 16M/2 = 8Mhz. Then you've got 1 start TQ, 1 propagation TQ, 5 segment 1 TQ, 3 segment 2 TQ for a total of 10 time quanta. 8000000 / 10 = 800,000 baud. You really need 16 TQ in order to attain 500,000 baud. So, try the following:
| Code: |
BRGCON1.brp = 1;
BRGCON1.sjw = 0;
BRGCON2.prseg = 2;
BRGCON2.seg1ph = 5;
BRGCON3.seg2ph = 5;
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Now it's 1 start, 3 prop, 6 seg1, 6 seg 2 for a total of 16 TQ. 16,000,000Mhz / 2 (baud prescaler) / 16 = 500,000 baud. |
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pic_beginner
Joined: 07 Feb 2011
Posts: 2
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| Posted: Thu Feb 10, 2011 11:06 am |
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thanks a lot  |
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Barrieri
Joined: 17 Feb 2016
Posts: 1
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| Posted: Wed Feb 17, 2016 2:46 am |
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Hi pic_beginner, have you solved your issue regarding the NOx sensor communication ? We are currently trying to communicate to a NOx module from a VW Golf, with a part number 5WK97308, however we are having a hard time trying to find our way. Any help would be greatly appreciated.
Regards |
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ezflyr
Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA
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| Posted: Wed Feb 17, 2016 5:55 am |
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Hi Barrieri,
Are you aware that the original thread is 5 years old?
Are you aware that this forum is exclusively for the CCS 'C' compiler? Are you using the CCS 'C' compiler?
Have a nice day!
_________________
John
If it's worth doing, it's worth doing in real hardware! |
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temtronic
Joined: 01 Jul 2010
Posts: 9221
Location: Greensville,Ontario
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| Posted: Wed Feb 17, 2016 6:44 am |
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Hmmm, I got curious about CAN TQ..... (OK I'm delaying snow shovelling...)
Downloaded a BOSCH paper on TQ...YEESH no wonder people have problems with CAN ! 10 friggin pages on how to create a BIT !
There must be a heckuva lot of 'overhead' per byte of data transferred.
Query. Does anyone know how many 'overhead' bytes to a 'data' byte there are?
Jay |
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RF_Developer
Joined: 07 Feb 2011
Posts: 839
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| Posted: Wed Feb 17, 2016 7:37 am |
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| temtronic wrote: | | Does anyone know how many 'overhead' bytes to a 'data' byte there are? |
CAN is a bit orientated protocol, therefore its not a question of how many bytes there are, its how many bits. With standard 11-bit addressing there are 44 "overhead", i.e. protocol-related bits, in a frame. It may carry 0 to 8
data bytes, i.e. 0 to 64 data bits. Its also bit-stuffed, and this may add some, or none, extra bits depending on the content of the frame, but no more than one extra bit for every five.
So a full frame is at least 108 bits long. For bus capacity and transmission latency purposes, I tend to estimate frames as 100 bits long for simplicty, and because many will not be full. So at 100kbs, a CAN bus could sustain bursts of 1000 messages per second, and each message takes at least 1ms to send, but in practice you can get no more than around 70% of that capacity, and that's if you're really careful. |
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