SI5351 start-up frequency

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Level42
 
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Joined: Sat Sep 03, 2016 5:33 pm

SI5351 start-up frequency

Post by Level42 »

Hi, I'm creating a project where I want to replace the (fixed) crystal of 16Mhz in a computer device with a variable frequency generator. The final product will be a dedicated PCB and it needs to be very small. For this reason I chose to go with a Digispark Attiny85 and an Adafruit Si5351 as a test set-up.

So far I have my Arduino Sketch running OK, I can select frequencies in steps of 1 Mhz and I checked the output with my oscilloscope. An OLED displays the freq. in 2 digits.

I have a few questions but start with this one:

The SI5351 datasheet says

5. Configuring the Si5351
The Si5351 is a highly flexible clock generator which is entirely configurable through its I2C interface. The device’s default configuration is stored in non-volatile memory (NVM) as shown in Figure 11. The NVM is a one time programmable memory (OTP) which can store a custom user configuration at power-up. This is a useful feature for applications that need a clock present at power-up (e.g., for providing a clock to a processor).

Power-Up


During a power cycle the contents of the NVM are copied into random access memory (RAM), which sets the device configuration that will be used during normal operation. Any changes to the device configuration after power-up are made by reading and writing to registers in the RAM space through the I2C interface


Sadly the datasheet does not mention HOW to program this....

Now, after I have everything running I want to remove the bootloader on the Attiny85 so it will start-up ASAP but I'm pretty sure my device needs the clock frequency "right away' so this NVM feature would be very needed.

Is it possible to program the NVM on the Adafruit board or is it already programmed ? If so...with what ? I would like it to fire up at the factory 16Mhz and then let the Attiny85 take control over the set frequency later.

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Level42
 
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Re: SI5351 start-up frequency

Post by Level42 »

I thought I had already posted this but I found the answer to my own question at Silabs forums:

The SI5351 can be ordered from Silabs with this default set-up. So this is not user changeable sadly.

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