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spi_xfer for more than 8 bits

 
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krugger



Joined: 12 Jul 2011
Posts: 18
Location: El Salvador

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spi_xfer for more than 8 bits
PostPosted: Fri Nov 25, 2011 11:59 am     Reply with quote
Hi everybody,

I'm working in a project in which I need to communicate a PIC 16F1827 with an VDIP2 module by FTDI.

This module uses a -let's say funny- SPI that needs 13 bits to be transmitted per each instruction (read or write, chronogram for a write instruction below).




I'm trying to develop the communication using SW SPI (#USE SPI and spi_xfer), but before using it in my project I've been experimenting with them in a dummy program.

I could send an arbitrary number of bits below 8 properly, but when I try to send more than 8 bits, only the last 8 are sent correctly and the others are simply not sent. This is the simple code of my program:

Code:

#include <SPI_VDIPsimple.h>
  #include <stdio.h>
  #include <stddef.h>
  #include <stdlib.h>
  #include <stdlibm.h>
  #include <string.h>
 
#USE SPI (MASTER, DO=PIN_B2, DI=PIN_B1, CLK=PIN_B4, ENABLE=PIN_B7, BAUD = 1000, MODE=2, BITS=13, ENABLE_ACTIVE=1, STREAM=VDIP, MSB_FIRST)



void main()
{

   setup_comparator(NC_NC_NC_NC);// This device COMP currently not supported by the PICWizard

   int cuatro=0b1010;
   int ocho = 0xFF;
   int doce = 0xFFF;
   int trece = 0b11001000101;
   
   spi_xfer(0xAA);

   spi_xfer(VDIP,cuatro,4);
   spi_xfer(VDIP,ocho,8);
   spi_xfer(VDIP,doce,12);
   spi_xfer(VDIP,trece,13);


}


and this is what I get when I try it in Proteus (I've checked it also with an osciloscope just to see if it was some kind of bug in Proteus and I obtain exactly the same)



(blue trace for SDO, red trace for SCK and green trace for CS)

What am I doing wrong? I'm using CCS 4.114.

Thank in advance for your time and help.

Pablo
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Nov 25, 2011 2:06 pm     Reply with quote
Quote:

int trece = 0b11001000101;

This can't work. An 'int' in CCS is different than ANSI C. It's an 8-bit
unsigned integer in CCS. Your number above is 11 bits.

Download the CCS manual.
http://www.ccsinfo.com/downloads/ccs_c_manual.pdf
Read this section. It explains CCS data types:
Quote:

Basic and Special types
krugger



Joined: 12 Jul 2011
Posts: 18
Location: El Salvador

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PostPosted: Fri Nov 25, 2011 3:27 pm     Reply with quote
Thanks PCM.

Changed the variables doce and trece for an int16 and works perfectly.

Sorry for the silly question.

Embarassed

Pablo
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