topic Re: LPC1313 SSP0 bit rate in LPC Microcontrollers

LPC1313 SSP0 bit rate

prachipanse — Wed, 03 May 2017 05:38:17 GMT

Hi,

I am trying to set the bit rate of the SSP0 port of the LPC1313FBD48/01 to 1MHz. The system clock is 72MHz, and it is divided by 12 to have the SSP clock as 6MHz. I have checked the CPSDVSR = 2 and SCR = 2, which should give me 1MHz:

Bit frequency = Pclk/(CPSDVSR * (SCR + 1))

However, I get 781.2kHz in place of 1MHz.

What might be going wrong here?

Regards,

Prachi

Re: LPC1313 SSP0 bit rate

jeremyzhou — Thu, 04 May 2017 02:26:14 GMT

Hi prachi panse,

Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.

I was wondering if you can share the screenshot of values of the corresponding registers under debugging.
Have a great day,
TIC

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Re: LPC1313 SSP0 bit rate

prachipanse — Thu, 04 May 2017 06:08:17 GMT

Hi,

I have tested with the same settings on another board and see that the bit clock gets set to 992kHz instead of 1MHz. The SSP0 registers are as below:

Please let me know if these values are as expected to achieve 1MHz bit rate.

Thanks and Regards,

Prachi

Re: LPC1313 SSP0 bit rate

jeremyzhou — Thu, 04 May 2017 07:33:59 GMT

Hi prachi panse,

Thank for your reply.

It's so weird, to dig the more deeper, can you share the wave of system clock via clkout pin?
Have a great day,
TIC

Re: LPC1313 SSP0 bit rate

prachipanse — Thu, 04 May 2017 08:39:19 GMT

Thanks. I have observed the system clock on the CLKOUT pin and it comes to be around 71-72MHz.

Re: LPC1313 SSP0 bit rate

jeremyzhou — Fri, 05 May 2017 01:44:40 GMT

Hi prachi panse,

Thanks for your reply.

If the system clock is located in the range of 71 to 72 MHz, the observed frequency: 992kHz can be considered correct according to below formula.

Bit frequency = Pclk/(CPSDVSR * (SCR + 1))

Hope it helps.
Have a great day,
TIC