topic Re: Using an external 32 KHz clock in 5606B in MPC5xxx

Using an external 32 KHz clock in 5606B

giladbarzilay — Wed, 25 Nov 2015 08:57:59 GMT

Hi there,

I am trying to use an external 32KHz clock on the EXTAL pin as the clock reference for the internal RTC in the 5606B chip.

I am working according to this table from the reference manual:

My OSC32_EXTAL pin is connected to a 32KHz clock (which is ticking correctly, verified with a scope), and OSC32_XTAL is grounded.

When I am setting the bypass bit in the SXOSC_CTL register (as per line 2) the RTC clock does not tick at all, and the API interrupt is never called, and when I set is to enable, and I am supposedly at line 4 of the table, the interrupt is called instead of every second, every ~1.3 seconds.

I measured the internal 32KHz clock using the CMU, and got a result of ~24KHz, which is consistent with the RTC behavior.

Tried on another board and replicated the results.

Any ideas on what I am doing wrong?

Thanks in advance.

Re: Using an external 32 KHz clock in 5606B

PetrS — Thu, 26 Nov 2015 14:36:35 GMT

Hi,

Do you use your own board or some FSL one?

I have tested the SXOSC with the RTC to generate 1sec interrupt on the TRK-MPC5606B and it worked if the SXOSC is enabled with SXOSC_CTL[OSCON] bit. The 32768Hz is fed to EXTAL pin and 1sec is properly generated.

BR, Petr

Re: Using an external 32 KHz clock in 5606B

giladbarzilay — Thu, 26 Nov 2015 14:59:03 GMT

Thank you for the reply.

I am using my own board, but like I said I verified the 32768Hz input with a scope.

Did you measure the 1 second frequency with an external indication / stopwatch? I am also getting the interrupts, only they are about 0.75 seconds apart instead of 1 second.

In addition, does bypass mode works for you?

Thanks again,

Gilad

Re: Using an external 32 KHz clock in 5606B

PetrS — Fri, 27 Nov 2015 13:16:36 GMT

Hi,

I measured the pin toggling with the scope, get 1sec exactly.

It is true that bypass mode worked in a strange way. The SXOSC_CTL[OSCON] has to be set too when bypass was set. In that case RTC was working too.

BR, Petr