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campbell.donald
Joined: 06 Apr 2010
Posts: 3
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| CAN Nodes With PIC16F877A and MCP2510 |
 Posted: Tue Apr 06, 2010 9:02 pm |
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Hello!
I am building a simple CAN bus with two identical nodes. Each node is made from a PIC16F877A, MCP2510, and an LT1796 transceiver.
I am using a 20 MHz oscillator on the MCP2510s.
I have set my timing as below:
| Code: |
#define CAN_BRG_PRESCALAR 1
#define CAN_BRG_PROPAGATION_TIME 3
#define CAN_BRG_PHASE_SEGMENT_1 8
#define CAN_BRG_PHASE_SEGMENT_2 8
#define CAN_BRG_SYNCH_JUMP_WIDTH 1
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Before I do anything, I call the following functions:
| Code: |
can_init();
can_set_mode(CAN_OP_NORMAL);
can_set_baud();
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My physical bus consists of a twisted pair of wires about 6 inches long, connecting the two LT1796 chips. Each LT1796 chip has a 120 Ohm resistor bridging the CAN_L and CAN_H signals.
When I run the "producer" node, it "successfully" sends three packets and then hangs. The "consumer" node never sees those packets, and simply does nothing.
Does anyone have any suggestions? I have checked my breadboard several times and all the pin connections appear to match those in can-mcp2510.h.
Thank you for your help! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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campbell.donald
Joined: 06 Apr 2010
Posts: 3
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| Posted: Tue Apr 06, 2010 9:20 pm |
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My code looks very similar to that. My concern is that I'm using a 20 MHz oscillator on the MCP2510, and therefore I need to fiddle with the bit timing.
If I set my bit timings to (what I think are incorrect) values, my producer successfully sends packets, but my receiver does not receive them.
Any suggestions?
| Code: |
#define CAN_BRG_PRESCALAR 1
#define CAN_BRG_PROPAGATION_TIME 1
#define CAN_BRG_PHASE_SEGMENT_1 3
#define CAN_BRG_PHASE_SEGMENT_2 3
#define CAN_BRG_SYNCH_JUMP_WIDTH 1
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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campbell.donald
Joined: 06 Apr 2010
Posts: 3
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| Posted: Tue Apr 06, 2010 10:04 pm |
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OK, thanks! It appears to work.
I ripped apart my previous code, removed my customized bit timings, and simplified its calls to can_putd and can_getd. Now it seems to work.
For anyone interested, I have posted my working code below:
| Code: |
#include <16F877A.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP,NOPUT,NOWDT,NODEBUG
#use delay(clock=20000000)
#include <can-mcp2510.c>
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#define PRODUCER 1
#define CONSUMER 0
#define ROLE CONSUMER
int main(void) {
int32 tx_id;
int8 tx_data[8];
int8 tx_len;
struct rx_stat rxstat;
int rx_len;
int8 rx_data[8];
int32 rx_id;
can_init();
can_set_mode(CAN_OP_NORMAL);
while(1) {
#if ROLE == PRODUCER
tx_id = 42;
tx_data[0] = 0x55;
tx_len = 1;
if (can_putd(tx_id, tx_data, tx_len, 3, TRUE, FALSE)) {
printf("Transmit OK. Successfully transmitted %x\n\r", tx_data[0]);
} else {
printf("Transmit FAILED.\n\r");
} // else
#else
if (can_kbhit()) {
if(can_getd(rx_id, &rx_data[0], rx_len, rxstat)) {
printf("Received packet from %x: %x\n\r", rx_id, rx_data[0]);
}
}
#endif
delay_ms(500);
}
return -1;
}
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