Hello everybody,

i'm busy with a school endassignment at a company. I need to build a
datalogger and i want to use a 8mbit atmel dataflash memory for storage. =
I'm
using a 16F877a pic mcu and the spi bus to acces it. I'm using the ccs
compiler. To test it i'm doing the following: put a value in buffer1 > re=
ad
it back > put buffer1 to a page > read the page back to buffer2 > reading
the value from buffer2 > also read the value direct from the page. Each t=
ime
i use printf to output the results to my pc to verify if everything went
right. The strange thing is that i can succesfully store my value in any
page i want, and read it back. But this only works when the byte address
(there are 264 bytes in a buffer and a page) is 0 to 18 and 256 to 265!
Every other byte address value leads to reading back "255" :-(  ........

I hope somebody can help me because it is a very strange problem and i've
already spent a day finding it.

Thanks a lot!

Vincent Blok
The Netherlands


Here are some pieces of the code i use to perform the reads and writes:
(it also doesn't work if i hardcode the adresses in stead of using variab=
le
names)

void df_write_b1(int8 value, int16 b_addr)
{
   int8 b_addr_l, b_addr_h;

   b_addr_l =3D make8(b_addr, 0);
   b_addr_h =3D make8(b_addr, 1);

   output_low(pin_b4);       =20
   spi_write(0x84);          =20
   spi_write(0x00);          =20
   #asm movf  0x13,w #endasm  //these seem to be necessary, i think it is=
 a
bug in ccs
   spi_write(b_addr_h);  =20
   #asm movf  0x13,w #endasm
   spi_write(b_addr_l);          =20
   #asm movf  0x13,w #endasm
   spi_write(value);        =20
   output_high(pin_b4);     =20
}

int8 df_read_b1(int16 b_addr)
{
   int8 rxspi, b_addr_l, b_addr_h;

   b_addr_l =3D make8(b_addr, 0);
   b_addr_h =3D make8(b_addr, 1);

   output_low(pin_b4);      =20
   spi_write(0xD4);         =20
   spi_write(0x00);         =20
   #asm movf  0x13,w #endasm
   spi_write(b_addr_h); =20
   #asm movf  0x13,w #endasm
   spi_write(b_addr_l);          =20
   spi_write(0x00);          =20
   rxspi=3Dspi_read(0);       =20
   output_high(pin_b4);     =20
   return rxspi;            =20
}

int8 df_read_b2(int16 b_addr)
{
   int8 rxspi, b_addr_l, b_addr_h;

   b_addr_l =3D make8(b_addr, 0);
   b_addr_h =3D make8(b_addr, 1);

   output_low(pin_b4);       =20
   spi_write(0xD6);        =20
   spi_write(0x00);         =20
   #asm movf  0x13,w #endasm
   spi_write(b_addr_h);  =20
   #asm movf  0x13,w #endasm
   spi_write(b_addr_l);        =20
   spi_write(0x00);          =20
   rxspi=3Dspi_read(0);        =20
   output_high(pin_b4);    =20
   return rxspi;            =20
}

void df_b1_to_page_e(int16 p_addr)
{
   int8 p_addr_l, p_addr_h;

   p_addr =3D p_addr << 1;
   p_addr_l =3D make8(p_addr, 0);
   p_addr_h =3D make8(p_addr, 1);

   output_low(pin_b4);
   spi_write(0x83);
   #asm movf  0x13,w #endasm
   spi_write(p_addr_h);
   #asm movf  0x13,w #endasm
   spi_write(p_addr_l);
   spi_write(0x00);
   output_high(pin_b4);
   delay_ms(23);
}

void df_page_to_b2(int16 p_addr)
{
   int8 p_addr_l, p_addr_h;

   p_addr =3D p_addr << 1;
   p_addr_l =3D make8(p_addr, 0);
   p_addr_h =3D make8(p_addr, 1);

   output_low(pin_b4);
   spi_write(0x55);
   #asm movf  0x13,w #endasm
   spi_write(p_addr_h);
   #asm movf  0x13,w #endasm
   spi_write(p_addr_l);
   spi_write(0x00);
   output_high(pin_b4);
   delay_us(310);
}

int8 df_page_read(int16 p_addr, int16 b_addr)
{
   int8 rxspi, p_addr_l, p_addr_h, b_addr_l, b_addr_h;

   p_addr =3D p_addr << 1;
   p_addr_l =3D make8(p_addr, 0);
   p_addr_h =3D make8(p_addr, 1);
   b_addr_l =3D make8(b_addr, 0);
   b_addr_h =3D make8(b_addr, 1);

   output_low(pin_b4);       =20
   spi_write(0xD2);          =20
   #asm movf  0x13,w #endasm
   spi_write(p_addr_h);      =20
   #asm movf  0x13,w #endasm
   spi_write(p_addr_l | b_addr_h);     =20
   #asm movf  0x13,w #endasm
   spi_write(b_addr_l);     =20
   spi_write(0x00);         =20
   spi_write(0x00);         =20
   spi_write(0x00);         =20
   spi_write(0x00);          =20
   rxspi =3D spi_read(0);     =20
   output_high(pin_b4);     =20
   return rxspi;            =20
}




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