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Erratic SPI with 16F876A and MCP2515

 
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iso9001



Joined: 02 Dec 2003
Posts: 262

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Erratic SPI with 16F876A and MCP2515
PostPosted: Sun Feb 19, 2006 10:32 pm     Reply with quote
Hi all,

I'm having some pretty big problems getting the SPI interface working. It seems I reset the 2515, read in CANCTRL and get 00, do another read and get 0x87, one more and I get 00 again. Somtimes that first 00 is an 0xFF.

I'de say maybe I'm having clock issues, but I'm using a 10MHz ceramic res with built in caps on the 2515 and a 20MHz version on the 16F876A pic. The pic seems stable. I don't have a scope of course Confused

Its REALLY frustrating.


Wondering if anyone had a similar problem or have any ideas,


Here some of the code I'm using:
Code:

void ResetMCP2515(void)
{
   output_high(MCP2515_CS);
   output_low(MCP2515_RESET_PIN);
   delay_us(10);
   output_high(MCP2515_RESET_PIN);
   delay_ms(0);
}

int ReadRegister(int regaddr)
{
   output_low(MCP2515_CS);
   spi_write(READCMD);
   spi_write(regaddr);
   rreg = spi_read(0);
   output_high(MCP2515_CS);
   return(rreg);
}


int data=0;
int data2=0;
int data3=0;

void main()
{
   setup_spi(SPI_MASTER | SPI_H_TO_L | SPI_XMIT_L_TO_H);

   ResetMCP2515();

   data3 = ReadRegister(CANCTRL);
   data2= ReadRegister(CANCTRL);
   data = ReadRegister(CANCTRL);


I've written it a few different ways. This code is borrowed from another post I saw.


Thanks in advance! [/code]
iso9001



Joined: 02 Dec 2003
Posts: 262

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PostPosted: Sun Feb 19, 2006 11:20 pm     Reply with quote
Here is my entire (crappy) code. Maybe there is somthing I'm missing.

Output: Which now seems to be pretty stable
Code:

Resetting CAN
Reading STAT : 80
Reading STAT : 0b
Reading STAT : 0f
Reading STAT : 03
Reading STAT : 03
Setting CTRL to 0x0F
Reading STAT : 00
Reading CTRL : 00


Program:
Code:

#include <16F876A.h>
#device ICD=TRUE
#fuses HS,NOLVP,NOWDT,NOPROTECT, PUT, NOBROWNOUT
#use delay(clock=20000000)
#use rs232(DEBUGGER)

#define CS        PIN_A4
#define RESET     PIN_A3
#define READCMD   0x03
#define WRITECMD  0x02

#define CANCTRL   0x0F
#define CANSTAT   0x0E


int data=99;
int tempdata,temp;


void CANReset(void)
{
   output_low(RESET);
   delay_us(10);
   output_high(RESET);
}


void CANWrite(int addr, int value)
{
   output_low(CS);
   spi_write(WRITECMD);
   spi_write(addr);
   spi_write(value);
   output_high(CS);
}


int CANRead(int addr)
{
   output_low(CS);
   spi_write(READCMD);
   spi_write(addr);
   tempdata = spi_read(0);
   output_high(CS);
   return(tempdata);
}


void main() {
output_high(CS); //Start CS high

setup_spi(SPI_MASTER | SPI_L_TO_H | SPI_XMIT_L_TO_H );


printf("Resetting CAN\n");
CANReset();


printf("Reading STAT ");
data = CANRead(CANSTAT);
printf(": %2x\n", data);

printf("Reading STAT ");
data = CANRead(CANSTAT);
printf(": %2x\n", data);

printf("Reading STAT ");
data = CANRead(CANSTAT);
printf(": %2x\n", data);

printf("Reading STAT ");
data = CANRead(CANSTAT);
printf(": %2x\n", data);

printf("Reading STAT ");
data = CANRead(CANSTAT);
printf(": %2x\n", data);


printf("Setting CTRL to 0x0F\n");
CANWrite(CANCTRL, 0x80);

delay_ms(10);

printf("Reading STAT ");
data = CANRead(CANSTAT);
printf(": %2x\n", data);

printf("Reading CTRL ");
data = CANRead(CANCTRL);
printf(": %2x\n", data);

 while (1) { }
}


I'm very stuck.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Feb 20, 2006 12:58 am     Reply with quote
Code:
#define CS        PIN_A4

One question to ask before looking at anything else, is do you have
a pull-up resistor on Pin A4 ?
iso9001



Joined: 02 Dec 2003
Posts: 262

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PostPosted: Mon Feb 20, 2006 3:08 am     Reply with quote
No,

I'm pulling it high then low then high again from the pic................

Oh sh!t ! IT GOT ME AGAIN!!!!!!!! ARRRRRRRR I AM SOOO FREAKING STUPID!!!

I H A T E THE A4 PIN!!!!

Seriously.... I'm a retarded desk rabbit !




I had it on A5 but when that was going on my code was crappy and it didn't anyway. So I moved it up one and didn't even think about it.

Thank You PCM, good catch. I'll try that tomorrow.
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