SPI Clock not working?

[SBS]

Hi,

I'm trying to set up an SPI port to communicate with an ADC. It doesn't appear to be working.

I am putting an oscillscope on the DO pin from the microcontroller and I am seeing a digital signal. However, when I put the oscilloscope on the clock pin, I see nothing.

Is there anything wrong with my code? The CCS help manual doesn't give ver much information about how the setup_spi command works.

Any suggestions?

Thanks,
Sal



#include <18F4620.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)


#define ADC_SELECT PIN_B1
#define ADC_DI PIN_C5
#define ADC_DO PIN_C4
#define ADC_CLK PIN_C3


void main() {

long int speed1;
long int speed2;
long int tempspeed;
BYTE data;

char display;

speed1 = 100;

setup_spi(SPI_MASTER | SPI_H_TO_L | SPI_CLK_DIV_16);

while (TRUE) {
printf(" _ ");
output_high(PIN_B0);
delay_ms(speed1);
output_low(PIN_B0);
delay_ms(speed1);


data = 0xFA;

spi_write(0x40);

data = spi_read();

}
}

[asmallri]

Where are you supplying the ADC with a chip select?
You may have to set the I/O direction to enable the SPI PINS. I do this by default but maybe the compiler does it automatically.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

[SBS]

Hi,

My ADC has its chip select tied low (active low).

I realized that I had my oscilloscope hooked up to the wrong signal. The ADC still isn't working yet, but now I have a better idea of what is going on.

With the code I posted, I am getting the correct digital output and the correct clock output pulses on the SPI_WRITE command. However, whenever I call SPI_READ, I do not see any clock pulses.

Any suggestions?

Thanks,
Sal

[Ttelmah]

You won't see clock pulses with a normal read.
SPI, is a two way bus. When you write a byte, a byte is _simultaneously_ read back. the 'read' command, just retrieves this byte (though see below). Remember also that the byte read back, is the _last_ one presented by the slave. So if you have a slave that responds with a byte from a command, you have to go:

[SBS]

Hi,

Thanks for your help. I've almost got it working now. I can write to and read from my ADC. However, my ADC is not responding yet.

I've tried both SPI_L_TO_H and SPI_H_TO_L. Looking at the SPI registers I see that the SPI modes that this function sets are:

SPI_L_TO_H
CPK=0
CPE=0

SPI_H_TO_L
CPK=1
CPE=1

Looking in the PIC manual (PIC18F4620) I have 4 supported SPI modes. The setup_spi command only appears to be able to utilize two of them.

What I need is the mode of:
CPK=0
CPE=1

This exactly matches the timing diagram in my ADC manual. Can I set up this SPI MODE with the CCS command? Or do I need to directly set the registers to get this functionality?

Thanks,
Sal

[PCM programmer]

http://www.ccsinfo.com/forum/viewtopic.php?t=22916&highlight=changespimode