Hello Forum,


I'm using the SPI of ATMega 1284(p) and need for creating a longer pulse 
a short switchoff of the intended SPI function.
The SPI is configured to be a master and works.

Unfortunately the SPI can't realy switched off, because i can't drive 
the MOSI (Pin B5) to Grounds.

My basic idea was: Get all registers back to initial value!

This don't work(!):

1

// Switchoff SPI Interface (to abtain control of lines)

2

3

      PRR0 |= (1<<PRSPI); // Disconnect Clock

4

      SPCR = 0;  // Init Value

5

      SPSR = 0;

If i  do not apply the commented line "Disconnect Clock" and leave it 
complet off like this:

1

// Switchoff SPI Interface (to abtain control of lines)

2

      SPCR = 0;  // Init Value

3

      SPSR = 0;

It works !
I don't find any hint in spec for switching off SPI !

Datasheet regarding  PRSPI:

1

Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface

2

3

Writing a logic one to this bit shuts down the Serial Peripheral 

4

Interface by stopping the clock to the module. 

5

When waking up the SPI again, the SPI should be re initialized 

6

to ensure proper operation.

I assume that the ATMEL need the clock to switch of (and load) the 
registers!

Did anybody out there share the same experiance ?

(Finding and fixing time appros 4 hours ! **grr**)

Regards Daniel