AnsweredHot!PIC32MZ EF Secondary Oscillator

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Benny32
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2018/05/15 12:28:18 (permalink)
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PIC32MZ EF Secondary Oscillator

Hello,
 
I'm currently making the schematic for my new PCB with a PIC32MZ1024EFG100 processor.
As I have read in the errata sheet a crystal oscillator can not be used for the secondary oscillator. Instead I have to use a external clock source.
 
The errata sheet (#4) specifies that the clock source has to be supplied to the SOSCO pin. Is that correct? Shouldn't it be the SOSCI pin? My second question is: Is it right, that the FSOSCEN bit have to be set to 0 instead of 1.
 
Thanks in advance for your help.
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Larry.Standage
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Re: PIC32MZ EF Secondary Oscillator 2018/05/15 15:32:33 (permalink) ☄ Helpfulby Benny32 2018/05/16 10:44:19
4.5 (2)
If you look at the oscillator diagram, you'll notice that the SOSCO pin leads to a buffer, which then goes into the main mux and Timer1/RTCC.
 
That's why the SOSCO pin has to be used. It's reflective of the inverter that would normally drive a crystal, but is where the signal leads into the chip.
 
 
 

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jcandle
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Re: PIC32MZ EF Secondary Oscillator 2018/05/15 16:30:10 (permalink)
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... which would require you to disable soscen and tristate the oscillator amp that would fight your external oscillator.  I am sure that is what the datasheet intends.
 
Alternately, you can feed sosci via a large resistor (assuming that the amp works at all - given the errata), enable the oscillator and let it drive the buffer.  At 32KHz there is little, if any, power differential.  
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Benny32
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Re: PIC32MZ EF Secondary Oscillator 2018/05/16 10:50:40 (permalink)
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Thanks for your replies.
 
Just one question: Why does the PIC32 reference manual says something different (section 42.3.1.3):
The SOSCI pin can be driven by an external 32.768 kHz clock source instead of using a crystal.
The SOSCEN bit must still be enabled; however, the SOSCO pin will be usable as an I/O.

 
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jcandle
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Re: PIC32MZ EF Secondary Oscillator 2018/05/16 10:56:40 (permalink) ☼ Best Answerby Benny32 2018/05/16 11:35:38
5 (1)
If you have had the unrivaled pleasure of writing datasheets for complex parts, you would be amazed at how few inconsistencies there are.  The "problem" is there are several ways to use the subsystem and datasheet writers do not want to confuse readers with all the options.
 
Option 1 - drive (s)osci with (s)oscen on to power up the oscillator amp. 
   a) Output the clock on (s)Osco as a buffered signal to the rest of the board
   b) Do not select the (s)Osco function and use the pin as GPIO or other function.
 
Option 2 - drive (s)Osco with a square wave with (s)oscen off to tristate and power down the oscillator amp.  Use (s)osci as a GPIO.
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Benny32
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Re: PIC32MZ EF Secondary Oscillator 2018/05/16 11:25:48 (permalink)
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That was really helpful for me. Thanks!
 
So everything is fine if I use a external oscillator and apply it's output to the SOSCO pin with a disabled FSOSCEN bit. Is that correct?
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jcandle
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Re: PIC32MZ EF Secondary Oscillator 2018/05/16 11:28:31 (permalink)
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That is how I understand the documents, their drawings, and general oscillator background... Given the errata I would go with that over the (s)osci and enabled methods.
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