Change SPI Clock

[rocket200]

Hello,

Is it possible to set and change the SPI Clock within a program? I need to do SPI at multiple clock speeds thorough my program. Would I somehow set the SPI Clock to a variable?

[Benj]

Hello,

I am not sure if you can change the SPI clock speed on the fly. It might be that you need to disable the module first before doing the speed modification and re-enabling.

To start I would try this and see if the clock speed changes.

In your program where you want to make a speed change use a C icon with code as follows.

sspcon = (sspcon & 0xF8) | FCV_SPIVAL;

In your Flowcode variable manager add SPIVAL as a byte variable and assign this with a value before you call the line of C.

Here are the various speed settings available on a 16F877A.

0 = Fosc / 4
1 = Fosc / 16
2 = Fosc / 64
3 = Timer2 / 2

You do have the option of using timer 2 as your clock source so maybe setting up the SPI like this and then changing the timer 2 properties would give you more control over the SPI speed.

[rocket200]

Hello,

I am not sure if you can change the SPI clock speed on the fly. It might be that you need to disable the module first before doing the speed modification and re-enabling.

To start I would try this and see if the clock speed changes.

In your program where you want to make a speed change use a C icon with code as follows.

sspcon = (sspcon & 0xF8) | FCV_SPIVAL;

In your Flowcode variable manager add SPIVAL as a byte variable and assign this with a value before you call the line of C.

Here are the various speed settings available on a 16F877A.

0 = Fosc / 4
1 = Fosc / 16
2 = Fosc / 64
3 = Timer2 / 2

You do have the option of using timer 2 as your clock source so maybe setting up the SPI like this and then changing the timer 2 properties would give you more control over the SPI speed.

Would this work on AVR?

[Benj]

No, This code was for a 16F877A. Which AVR are you using?

[rocket200]

No, This code was for a 16F877A. Which AVR are you using?

I'm using the ATTiny2313.

[Benj]

Hello,

You can force the SPI on the ATtiny to run based on a timer 0 interrupt. Would this be any use to you?

I think to do this you would need to use the following C command.

Code: Select all

USICR = (USICR & 0xf3) | 0x04;

Or you can setup the SPI rate to be software controlled using this command.

Code: Select all

USICR = (USICR & 0xf1) | 0x02;

Then use this command to increment the SPI clock, each SPI transaction will require 8 clock pulses.

Code: Select all

USICR = (USICR & 0xfd) | 0x02;

Let me know how you get on.