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!

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

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Reply to
Spehro Pefhany

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.

That instruction is backwards from your C statement.

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John W. Temples, III
Reply to
John Temples

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