MSP430f5529 Launchpad, Energia SPI clock rate

Mel Martin

Other Parts Discussed in Thread: ENERGIA, MSP430F5529

I'm using this Launchpad for SPI communication with a device that has a max SCLK rate of 50kHz. I 've tried using the SetClockDivider, but I don't think that I'm able to divide the DCO to ~40kHz. Is my assumption correct? If so, would I have to supply from ACLK, and if so how would I implement this in energia code?

Thanks,

Mad Max

over 9 years ago

0 Dennis Eichmann over 9 years ago

Guru 74080 points

Hi Max!

I don't know this Energia stuff, but the divider for the USCI modules are very versatile. It is made of

BR0 + (BR1 * 256)

Let's say your MSP430F5529 would run at it's maximum of 25MHz, then for having a SPI clock of 50kHz, you would need a divider of

25000000 / 50000 = 500

That would mean you would have

BR1 = 500 / 256 = 1

BR0 = 500 - (BR1 * 256) = 500 - 256 = 244

That's it. But as I said - I don't know how this is done with Energia.

Dennis

0 Clemens Ladisch over 9 years ago in reply to Dennis Eichmann

Guru 317320 points

Energia's SPI.setClockDivider() ends up setting exactly these registers:

	UCB0BR0 = clkdiv & 0xFF;
	UCB0BR1 = (clkdiv >> 8 ) & 0xFF;

Just call it with a divider of 500, or whatever you need.

0 Mel Martin over 9 years ago in reply to Clemens Ladisch

Prodigy 60 points

That maximum integer, as listed on energia site, is 255. If I set anything over this it seems to default to fastest clock speed.

Max

0 Dennis Eichmann over 9 years ago in reply to Mel Martin

Guru 74080 points

Can you post a link to the documentation you refer to? And if it is limited by the function, doesn't Energia allow to access the registers directly, so you can write to BR0 and BR1 yourself? Which clock speed do you have? With 255 you could still use 12.75MHz as input to get 50kHz out.

Dennis

0 Clemens Ladisch over 9 years ago in reply to Mel Martin

Guru 317320 points

Which site says that for the LaunchPad?

0 Mel Martin over 9 years ago in reply to Clemens Ladisch

Prodigy 60 points

It's not specifically about the launchpad, but may be a limitation of the energia libary "SPI_SetClockDivider".
energia.nu/.../

Max

0 Mel Martin over 9 years ago in reply to Clemens Ladisch

Prodigy 60 points

It may just be a limitation of the Energia IDE SPI_SetClockDivider library since it was originally programmed for the Arduino Due.
energia.nu/.../

Max

0 Mel Martin over 9 years ago in reply to Dennis Eichmann

Prodigy 60 points

Dennis,

That did the trick, I was able to set it manually as you instructed. Thank you the help.

0 Akash Patel over 9 years ago

TI__Expert 6245 points

Hi Max,

As Dennis Eichmann pointed out, you can modify the BR0 and BR1 registers in order to set the divider. Before you modify them, you have to enable the UCSWRST bit which can be done through the CTL1 register. These registers are explained in pages 980-981 of the user's guide (http://www.ti.com/lit/ug/slau208o/slau208o.pdf)

You can modify the registers directly in Energia. If you're using a 25 MHz clock and want to divide it to 50 kHz (divider = 500), you can use the following to set the registers in Energia:

UCA0CTL1 |= UCSWRST; // enable software reset, USCI logic held in reset state
UCA0BR0 = 244;
UCA0BR1 = 1;
UCA0CTL1 &= (~UCSWRST); // disable software reset, USCI reset released for operation

Best Regards,

Akash Patel

0 Clemens Ladisch over 9 years ago in reply to Akash Patel

Guru 317320 points

Or instead of setting these registers directly, you could just call setClockDivider().

The MSP430 hardware supports larger divders; the setClockDivider() function does so, too. (The implementation is correct, but nobody bothered to update the documentation.)

0 Akash Patel over 9 years ago in reply to Clemens Ladisch

TI__Expert 6245 points

Clemens,

Max said he tried this and it wouldn't work for him. On the Energia website, it says 255 is the highest parameter. http://energia.nu/reference/spi/spi_setclockdivider/

Regards,

Akash Patel

0 Clemens Ladisch over 9 years ago in reply to Akash Patel

Guru 317320 points

No; the question does not contain an actual observation, and the Energia website does not say anything about the MSP430 implementation.

0 AIGun over 9 years ago

Prodigy 20 points

0 Clemens Ladisch over 9 years ago in reply to AIGun

Guru 317320 points

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MSP430f5529 Launchpad, Energia SPI clock rate