PIC 18F4520 SPI with Serial EEPROM

I am attempting to communicate with a 25LC256 serial (SPI) EEPROM with a
18F4520.  I have successfully communicated with this same EEPROM with a
18F4431 using the same code.

The code I am using is as follows:

MEM_CS = 0;

SSPBUF = 0x02;
while(SSPSTATbits.BF != 1);
SSPBUF = AddressHigh;
while(SSPSTATbits.BF != 1);
SSPBUF = AddressLow;
while(SSPSTATbits.BF != 1);
SSPBUF = DataByte;
while(SSPSTATbits.BF != 1);

MEM_CS = 1;

I have connected a scope on the SDO line of the microcontroller.  I see the
0x06 clocked out followed by 3 zeros...no matter what the values of
AddressHigh, AddressLow, and DataByte are.  I notice from the In-Circuit
Debugger that after this transfer, the collision bit gets set somewhere.  I
have tried replacing the 3 variables with fixed values and everything works
fine (the correct fixed values are transmitted from the SDO pin).

I see in the dissassembly listing that the "SSPBUF = AddressHigh"
instruction is represented using...

MOVFF {SSPBUF}, {AddressHigh}
NOP

where the brackets represent the address of SSPBUF and AddressHigh.

Am I missing something here?  Is this a problem with the microcontroller
itself or with the compiler?  I have ruled out a connection problem because
everything works fine when using fixed values.

Thanks!

On Wed, 17 May 2006 21:40:57 -0500, the renowned "Patrick Johnson"
<kirilian@bellsouth.net> wrote:

>I am attempting to communicate with a 25LC256 serial (SPI) EEPROM with a
>18F4520.  I have successfully communicated with this same EEPROM with a
>18F4431 using the same code.
>
>The code I am using is as follows:
>
>MEM_CS = 0;
>
>SSPBUF = 0x02;
>while(SSPSTATbits.BF != 1);
>SSPBUF = AddressHigh;
>while(SSPSTATbits.BF != 1);
>SSPBUF = AddressLow;
>while(SSPSTATbits.BF != 1);
>SSPBUF = DataByte;
>while(SSPSTATbits.BF != 1);
>
>MEM_CS = 1;
>
>I have connected a scope on the SDO line of the microcontroller.  I see the
>0x06 clocked out followed by 3 zeros...no matter what the values of
>AddressHigh, AddressLow, and DataByte are.  I notice from the In-Circuit
>Debugger that after this transfer, the collision bit gets set somewhere.  I
>have tried replacing the 3 variables with fixed values and everything works
>fine (the correct fixed values are transmitted from the SDO pin).
>
>I see in the dissassembly listing that the "SSPBUF = AddressHigh"
>instruction is represented using...
>
>MOVFF {SSPBUF}, {AddressHigh}
>NOP
>
>where the brackets represent the address of SSPBUF and AddressHigh.
>
>Am I missing something here?  Is this a problem with the microcontroller
>itself or with the compiler?  I have ruled out a connection problem because
>everything works fine when using fixed values.
>
>Thanks!

Try using the SSPIF flag rather than BF. BF is only valid in SPI slave
mode reception AFAUI. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

On 2006-05-18, Patrick Johnson <kirilian@bellsouth.net> wrote:
> I am attempting to communicate with a 25LC256 serial (SPI) EEPROM with a
> 18F4520.  I have successfully communicated with this same EEPROM with a
> 18F4431 using the same code.
>
> The code I am using is as follows:
>
> SSPBUF = 0x02;
> while(SSPSTATbits.BF != 1);
> SSPBUF = AddressHigh;
> while(SSPSTATbits.BF != 1);
> SSPBUF = AddressLow;
> while(SSPSTATbits.BF != 1);
> SSPBUF = DataByte;
> while(SSPSTATbits.BF != 1);

Are you sure that writing to SSPBUF clears BF?  I'm under the
impression that happens only with a read, not a write.  I would expect
your code to fall through the second and subsequent while loops.

> I see in the dissassembly listing that the "SSPBUF = AddressHigh"
> instruction is represented using...
>
> MOVFF {SSPBUF}, {AddressHigh}
> NOP
>
> where the brackets represent the address of SSPBUF and AddressHigh.

That instruction is backwards from your C statement.

-- 
John W. Temples, III