Syntax:
FVRInitialize ( FVR_OFF | FVR_1x | FVR_2x | FVR_4x )
Command Availability:
Available on all Microchip microcontrollers with the Fixed Voltage Reference (FVR) module.
Explanation:
The method is a subroutine that sets the state of the FVR.
FVR_Off = Fixed Voltage Reference is set to OFF
FVR_1x = Fixed Voltage Reference is set to 1.024v
FVR_2x = Fixed Voltage Reference is set to 2.048v
FVR_4x = Fixed Voltage Reference is set to 4.096v
Using the the following device’s datasheet, as a general case, http://ww1.microchip.com/downloads/en/DeviceDoc/40001419F.pdf that can be downloaded from the device’s page, http://www.microchip.com/wwwproducts/en/pic16f1828 parameter AD06 in table 30-8 at page 359, and the corresponding Note 4, tell us that the Vref voltage (Vref+ minus Vref-) should not be less than 1.8V, regardless of the reference voltage used, in order for the ADC module to work within the datasheet specifications. Also, as Vref- cannot be a negative voltage (voltages below GND) the lowest voltage on it is 0V. Then an FVR of 1.024V cannot be used as VREF+ for the ADC, but only 2.048 and 4.098 values.
The 1.024V FVR value exists for usage with other modules not just the ADC module.
Example:
'// use FVR 4096 as Reference
FVRInitialize ( FVR_4x )
wait while FVRIsOutputReady = false
ADVal = ReadAd(AN0)
'// Turn off FVR
FVRInitialize ( FVR_Off )For more help, see FVRIsOutputReady
