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SPI problems while connecting PIC18F452 to MCP3208 ADC

 
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jjacob



Joined: 08 Mar 2008
Posts: 54
Location: PORTUGAL (PORTO)

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SPI problems while connecting PIC18F452 to MCP3208 ADC
PostPosted: Thu Aug 28, 2008 12:46 pm     Reply with quote
Hi,

i'm trying to read 8 analog signals. So i found MCP3208 who has a SPI interface. I've never worked with SPI and can't get the right values of ADC inputs. I've looked in forum but i couldn't find out the solution.

My version of PCH Compiler is 4.057.

My problem is that the only result that i can get i 0 (zero) in the three readings of SPI.
I've connected the Vref of MCP3208 to Vcc (5v) and i force (with an ampop for low output impedance) 2.5V in CH0.

This is my code :

Code:
#include <18F452.h>

// -----------------------------
// ICs interconnections
// -----------------------------
// PIC   Descr      MCP3208   Descr
// -----------------------------
// 24   SDO         11      SDI
// 23   SDI         12      SDO
// 18   SCK         13      CLK
// 17   RC2         10      ~CS/SHDN

#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
//#use spi(MASTER, MODE=3, BITS=8, FORCE_HW, ENABLE=PIN_C2)
#use spi(MASTER, MODE=1, BITS=8, FORCE_HW, ENABLE=PIN_C2)

//#define CS PIN_C2

int8 read1, read2, read3;

void main(void)
{
// If i don't delay here, the printf doesn't print....
delay_ms(1);

printf("\r\nTesting Serial\r\n");
delay_ms(1000);

   while(true)
   {
   // Select CH0 (send 6 + 0 + X) (pag. 15 of MCP3208 datasheet)
      spi_write(6);
      spi_write(0);
      spi_write(0);

      //while(!spi_data_is_in());
            read1 = spi_read();
     
       //while(!spi_data_is_in());
             read2 = spi_read();

       //while(!spi_data_is_in());
             read3 = spi_read();

      printf("\r\nFirst : %d, Second : %d, Third : %d\r\n", read1, read2, read3);
      
      delay_ms(100);   

   }
}


I've tested with MODE=3...
Can anybody help me to get the right values of MCP3208.

Thank you in advance.
Jacob
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Aug 28, 2008 1:00 pm     Reply with quote
I suggest that you don't use the "#use spi()" method. Just use the
setup_spi() function. We know that it works.

Read my post in this thread about how to setup up the correct mode,
and especially, how to use the spi_read() statement to read a byte.
http://www.ccsinfo.com/forum/viewtopic.php?t=35566

Also, I notice that you're using inline code for your driver. I suggest
that you duplicate the functions in the CCS driver (which uses software
SPI), and change the "guts" of each function to use hardware SPI.
Here's the driver location:
Quote:
c:\program files\picc\drivers\mcp3208.c
jjacob



Joined: 08 Mar 2008
Posts: 54
Location: PORTUGAL (PORTO)

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PostPosted: Thu Aug 28, 2008 4:45 pm     Reply with quote
Thank you PCM programmer.

I'm quite new with CCS and i should have looked to the drivers...
I will try to change from 'Software' to 'Hardware' SPI but i'm not an expert...

If i change :

Code:
#define MCP3208_CLK  PIN_B0
#define MCP3208_DOUT PIN_B1
#define MCP3208_DIN  PIN_B2
#define MCP3208_CS   PIN_B3


to the Hardware pins wouldn't work ? (Sorry if this is a basic question ...)

Somewhere in this forum, you said that if we use the hardware pins in the software implementation it would not work... something like this ...

I've read the files that you said... but for the moment is not easy to change the code 'guts'... but i'll try Smile

Thank you.
Jacob
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Aug 28, 2008 5:06 pm     Reply with quote
The hardware SPI pins (SCLK, SDO, SDI) are specified in the PIC data
sheet. The only pin that you can assign is the \CS signal.

If you are translating a software driver to hardware, then just delete
the #define statements for CLK, DOUT and DIN. You don't get to
decide on them. They are not even referenced in the hardware SPI
driver code. The pin assignments are implicit. When you put in
the line "spi_write(0x55);", you are inherently specifying that the
data (0x55) will go out on the SDO pin of the PIC.
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