Hi
I've been trying to change the external reference voltage (VREF-HI) for the ADC, on my F28035 DIMM controlCard with the Experimenter Kit
Inside InitAdc, of DSP2803x_Adc.c file I've added
AdcRegs.ADCCTL1.bit.ADCREFSEL = 1;
So the complete code is:
EALLOW;
AdcRegs.ADCOFFTRIM.bit.OFFTRIM = 0x1DA;
AdcRegs.ADCCTL1.bit.ADCBGPWD = 1; // Power ADC BG
AdcRegs.ADCCTL1.bit.ADCREFPWD = 1; // Power reference
AdcRegs.ADCCTL1.bit.ADCPWDN = 1; // Power ADC
AdcRegs.ADCCTL1.bit.ADCENABLE = 1; // Enable ADC
EDIS;
And I've switched the pin SW3 in the "upward" position, on my controlCard.
"Position 1 controls VREF-HI, the value that the ratiometric ADC will convert as the maximum 12-bit value, 0X0FFF. In the downward position, VREF-HI will be connected to 3.3V. In the upward position, VREf-HI will be connected to pin 66 of the DIMM100-socket."
It seems to change for an external reference of 2.048V, with my experimenter kit.
But I would like to change it for an external reference of 1.024V
According to the file "An Overview of Designing Analog Interface With TMS320F28xx/28xxx DSCs", that's something I can do
For F280xx devices: The ADCREFIN voltage (1.024 V, 1.500 V, or 2.048 V) replaces the internal BG voltage, which is then used to generate the signals REFP/REFM that are used by the ADC during the conversion process.
How can I achieve it?
Thanks!
Jerome,
The F2803x ADC does not have a fixed value for VREFHI in external reference mode as ADCREFIN does on the F280x. VREFHI can be any value between 2.64v and the VDDA rail, or 1.98v and VDDA if VREFLO = 0v. Refer to the data manual on p.120: http://www.ti.com/lit/gpn/tms320f28035
The F2803xp ADC user's guide has more information on using the external reference mode: http://www.ti.com/litv/pdf/spruge5a
Regards,
Nicholas Smith