Analog Functions and Additions

wiring_analog after V1.2.1

Analog functions like analogRead and analogWrite etc. have changed after V1.2.1 to have extra safety measures to ensure invalid settings cannot be done and report errors.

Additionally extra getter functions have been added so other libraries can access the resolution of read and write functions as number of bits and current maximum value possible.

Extra functions

These functions return the analogue resolution as number of bits

• uint8_t getAnalogReadBits( ) - range 8 to 12
• uint8_t getAnalogWriteBits( ) - range 8 to 16

These functions return the analogue resolution as its maximum value

• uint16_t getAnalogReadMaximum( ) - range 255 to 4095
• uint16_t getAnalogWriteMaximum( ) - range 255 to 65535

This function enables the analog amplifiers at the ADC inputs with adjustible gain (for XMC1000 series)

• uint32_t analogRead_variableGain( uint8_t channel, uint8_t gain_value )
  The gain factor values can be found here.

Default Values

Read resolution default is 10 bits (0 to 1023)

Write resolution default is 8 bits (0 to 255)

Error and Return Codes by Function

Where possible functions do NOT action invalid parameters passed in.

Functions return error codes or valid values so be sure which error code you are looking for as some functions can return 0 as a valid value (e.g. analogRead) so an out of range value is returned instead.

Function	Valid Return	Errors
analogReadResolution	8 to 12 as passed in	255
getAnalogReadBits	8 to 12	none
getanalogReadMaximum	255 to 4095	none
analogWriteResolution	8 to 16 as passed in	255
getAnalogWriteBits	8 to 16	none
getanalogWriteMaximum	255 to 65535	none
analogRead	0 to Maximum for Resolution	0xFFFFFFFF usually invalid channel
analogWrite	0 success	-1 = invalid value -2 = wrong pin
setAnalogWriteFrequency	0 success	-1 = invalid frequency -2 = wrong pin
analogReference	none	NULL function see below

This should enable checks in software for valid operation and debugging problem code.

AREF Analogue Reference

On all boards the Analogue Reference is set to use the internal power supply (however noisy), so the AREF pin is an OUTPUT of the AREF in use. Do NOT connect any external voltage source to this pin, or use shields that change this voltage.

CAUTION any shorts on this pin especially to 0V (GND) will bring down the supply of the chip.

The pin voltage is the current supply voltage to AREF for analogue conversions.

This pin CANNOT be reassigned as GPIO (pinMode has no effect).

analogReference( )

This function has NO operation and will not match any call on parameters passed in with other libraries or examples that use this call.

Any shields and examples that try to change this, will NOT function the same on these boards.

Analog amplifiers at the ADC inputs with adjustible gain

Each analog input channel can be configured to be amplified by an adjustable gain factor, for XMC1000 series. To configure the gain, the gain value is to be selected in the analogRead_variableGain() function which translates to a gain factor as per the following table:

Gain value	Gain factor
0	1
1	3
2	6
3	12

For more information, please refer to the application note here.

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