S08FL16 A/D issues

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S08FL16 A/D issues

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tonyp
Senior Contributor II

The MC9S08FL16RM(.PDF) rev 3 says FL16 has 12channel 8-bit A/D (but not 10-bit or 12-bit).

 

The A/D module used, however, is the S08ADC12V1 which is the same used in QE128/QE32 etc, and certainly has 10-bit and 12-bit capability in the QE's.

 

The same reference manual says that ADCCFG mode bits can be configured for 8, 10, or 12-bit operation (with no note about the 10 and 12 options being unavailable for the FL16), implying that all configurations are possible.

 

The register summary, however, shows ADCRH location ($0002) in the memory map as reserved (as well as the remaining higher than 8 bit A/D related registers).

 

But the mc9s08fl16.inc for CW has ADCRH (and the rest of the registers) defined in the reserved location ($0002).

 

So, which is it, my dear Freescale people?  Make up your mind: Does the FL16 support only 8-bit A/D, or more?

 

And, (assuming 8-bit is the correct answer) my next question is this:

 

What happens if the mode bits are set for 10-bit or 12-bit operation.  Will I get 8-bit result, or undefined operation?

 

Thank you.

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david_diaz
NXP Employee
NXP Employee

Hello Tony,

Please note that the packages of the S08FL sub-family were designed for are smaller pin count. 

They lack dedicated VDDA, VSSA, VREH and VREFL pins.  The design was done to make it less costly but still offer the ADC input. 

Also notice that generally parts with higher resolution have these pins in some combination.  These pins are required for better resolution to reduce the digital noise on the ADC. 

I assume the module will work if you set it with different resolutions, but Freescale does not guaranty the best accuracy due to the situations mentioned above.

I recommend set this device as the documentations suggest.

Hope this information will be useful for you.

Have a great day.

David