S12G VDDF for ADC calibration

[jinjingyang]

Dear Sir,

According to S12G datasheet "1.17 ADC Result Reference", we can read ADC channel internal_0 to get the VDDF voltage.

With the converted  VDDF value and the stored VDDF value, we can calculate the accurate VRH.

There are following questions:

1) The stored VDDF is at 0x4022/0x4023.

Does this mean  that this value is erased when we erase and program the S12G MCU in CodeWarrior?

We cannot  erase the 0x4000 flash sector if  we want to use this feature?

2) According to the note:

"This implies that code must be executed from RAM. The “ConvertedReference” value must be the average of eight consecutive conversions."

It's just internal ADC channel sampling and conversion, not flash  erase and programming.Why does it have to execute in RAM for ADC operation? 

3) According to datasheet "Table A-30. Voltage Regulator Characteristics":

VDDF = 2.6V ~ 2.82V ~ 2.9V. Is this the voltage range for -40~125degC? It's the voltage spread across all parts?

Since the error for VDDF within -40~125degC is +/-20mV, does it mean that VDDF can be 2.6V~2.9V and the stored VDDF value at 0x4022~0x4023 follows the +/-20mV error. It doesn't mean VDDF = 2.80V~2.84V.

Regards,

Jason Yang

[RadekS]

Hi Jason,

1. You are right, it is a confusing statement. There should be rather “at global address 0x0_4022/0x0_4023 in the NVM’s IFR”

The IFR field will be visible in memory map after we set MMCCTL1_NVMRES bit and it is accessible at page 0x01 in memory window from 0x8000. So, the local address will be 0x018022~0x018023.

2. The VDDF is a device internal supply output of the voltage regulator that provides the power supply for the NVM logic. So, flash operations may slightly influence current VDDF voltage (executing code from flash = reading operations at flash).

Note: The newer S12 MCUs have implemented internal channel for ADC measurement of bandgap voltage instead of VDDF.

3. This 2.6V ~ 2.82V ~ 2.9V voltage range is valid across all parts in Junction Temperature range from –40°C to +160°C. It also includes safety margins.

If the target VDDF voltage at one specific MCU is 2.82V, we guarantee that VDDF will stay in range 2.80V~2.84V across temperature range -40~125degC. However, the next MCU may have VDDF voltage for example 2.72V (2.70V~2.74V). Therefore the factory measurement is performed at every single MCU and stored into their NVM’s IFR field.

I hope it helps you.

Have a great day,
Radek

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