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Nora
Joined: 23 Mar 2008
Posts: 50
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| SPI problem (not even clock) with PIC18F452 |
 Posted: Sat Feb 19, 2011 1:15 pm |
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Hello-
I am trying to get SPI communications working with a PIC18F452. I do not even get clock. My oscilloscope is able to read 10MHz signal (on slave transceiver) but seems to stop the chip's operation (I have a blinking LED) when I put it to read on the PIC's 20 MHz external oscillator.
Therefore, I used the SPI_CLK_DIV_64, hoping that this means that the SPI clock signal is 20 MHZ / 64 = 312 KHz... so if I am understanding this correctly, I should be able to read the clock signal.
I am reading all over this forum that it is best not to use both setup_SPI and #use spi at the same time. True?
I'm using the pins that the PIC says to use for SPI : C3 = SCK, CC4 = SDI, C5 = SDO
When I uncomment the #use spi, the word "DO" goes navy blue.
???
SPI_Write() can only put out 8 bits? What if I need to send 16 bits all at once? Should I use the SPI_XMIT function? Does it send LSB or MSB first?
I guess the biggest problem is no clock signal. So I can't even get to the rest to troubleshoot. Hoping there is just some simple setting that I got wrong. I did not do anything with the SPI pins (ie: no extra hardware).
Here's the code. All I am trying to do at this point is get a clock output.
Thanks in advance,
Nora
| Code: |
#include <18F452.H>
#fuses HS,NOWDT,NOPROTECT,BROWNOUT
#use delay(clock=20000000) // one instruction=0.2us
#include <stdlib.h>
//#include <math.h>
//#use spi(Di=PIN_C4, Do=PIN_C5, CLK=PIN_C3)
//BITS = 16, BAUD = 9600,
#define SPI_MODE_0 (SPI_L_TO_H | SPI_XMIT_L_TO_H)
#define SPI_MODE_1 (SPI_L_TO_H)
#define SPI_MODE_2 (SPI_H_TO_L)
#define SPI_MODE_3 (SPI_H_TO_L | SPI_XMIT_L_TO_H)
//***********************************************************
void main()
{
//set_tris_c(0x00);
// sets transmitter up as master (master generates clock), low to high clock transmission
setup_spi(SPI_MASTER | SPI_MODE_0 | SPI_CLK_DIV_64);
while(1){
//spi_write(0b1000000010110000); //
//spi_write(0x38);
//delay_ms(100);
output_low(PIN_A5);
delay_ms(1000);
output_high(Pin_A5);
delay_ms(1000);
}
} |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Feb 19, 2011 1:25 pm |
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Run a simple test program. Then look at Pin C3 for the SPI clock.
Example:
| Code: |
#include <18F452.h>
#fuses HS, NOWDT, PUT, BROWNOUT, NOLVP
#use delay(clock = 20000000)
#define SPI_MODE_0 (SPI_L_TO_H | SPI_XMIT_L_TO_H)
#define SPI_MODE_1 (SPI_L_TO_H)
#define SPI_MODE_2 (SPI_H_TO_L)
#define SPI_MODE_3 (SPI_H_TO_L | SPI_XMIT_L_TO_H)
//========================================
void main()
{
setup_spi(SPI_MASTER | SPI_MODE_0 | SPI_CLK_DIV_64);
while(1)
{
spi_write(0x55);
delay_us(100);
}
} |
Don't run it in Debug mode. Don't attempt to step through the code.
Compile and run it in Release mode. You should see the SPI clock. |
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Nora
Joined: 23 Mar 2008
Posts: 50
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| Posted: Sat Feb 19, 2011 1:33 pm |
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I DO see the clock.
Thanks! |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19337
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| Posted: Sat Feb 19, 2011 4:17 pm |
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And, on sending 16bits, just send two lots of 8bits. The _hardware_ only sends 8bits at a time, and if you load a new byte immediately, the transaction is effectively 'non stop' (which shouldn't matter anyway with SPI - this is why it sends a clock...).
Best Wishes |
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