Deviations from Arduino Language Reference

Functions and Options Differences

Extra modes (if patches applied)

This section covers the differences between standard Arduino and XMC-for-Arduino

GPIO

Extra pinMode types added that most engineers want

INPUT_PULLDOWN
OUTPUT_OPENDRAIN

Extra functions (than standard Arduino AVR)

GPIO

Does what the function names says but must have been configured as output

digitalToggle( pin )

Arduino Function Differences

Input Mode Pins

On standard Arduino boards, GPIO is by default either a function like Serial or in INPUT mode.

On XMC boards the inputs are UNDEFINED, you MUST specify every pin to be in INPUT Mode that needs Inputs.

Interrupt

XMC1400 Kit for Arduino - Interrupt 1 pin allocated to pin number - 7 .. code-block:

const byte interruptPin = 7; // for interrupt-1

Wire/I2C Differences

The method in Wire class for ‘begin’ is not the same as AVR Arduino, and has different modes for Master and Slave

In AVR Arduino setting an I2C Master or Slave

Wire.begin(8); // join i2c bus (address optional for master)

XMC-for-Arduino setting for I2C Master ONLY

Wire.begin(); // join i2c bus (address blank for master)

Currently the address is NOT optional for XMC as this currently assumes this must be Slave mode configuration and sets the I2C configuration differently.

Tone

Number of Tone pins is determined by pins_arduino.h define NUM_TONE_PINS. This allows for use in other modules and for variations between boards as >100MHz boards can obviously handle more tone pins.

The default for XMC1xxx is 4 with a change XMC4xxxx should be 16

Tone has frequency range of maximum = 500 Hz minimum = 1 Hz

Due to the Systick periodicity, only discrete frequencies are supported as listed below: [1, 2, 4, 5, 10, 20, 25, 50, 100, 125, 250, 500]

This is due to the fact that the tone frequency is software derived from the Systick handler, Systick has a time period of 1 ms. At maximum each handler event for Systick toggles a GPIO pin, so at minimum period of 1 ms the output is toggled, so TWO events produce one square wave cycle, therefore the maximum output frequency is 500Hz.

The minimum is due to the fact that tone function only accepts an unsigned integer (32 bit) for the frequency, so the minimum usable frequency is 1.

Standard Arduino boards use hardware timers (the few that are available) to generate tones and at least one timer can interfere with other functions.

However this does mean you can have more tone pins, just much lower frequency range.

Analog Functions

Resolution

Read resolution default is 10 bits (0 to 1023) You can set the read resolution to 8, 9, 10, 11 or 12 bits using the analogReadResolution( bits ) function, where bits is the number of bits you want to set the resolution to.

Write resolution default is 8 bits (0 to 255) You can set the write resolution to 8, 9, 10, 11, 12, 13, 14, 15 or 16 bits using the analogWriteResolution( bits ) function, where bits is the number of bits you want to set the resolution to.

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

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

analogReference( )

This function has only one defalut mode DEFAULT = 3.3V 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.

DAC Analog Output

analogWrite( )

This API usually Writes an analog value (PWM wave) to a pin. Some XMC4 boards have true analog output capabilities on the DAC enabled pins.

The DAC output voltage range for the XMC4000 series is limited to a minimum of 0.3V and a maximum of 2.5V.

Note

The following example formula can be used to convert the target voltage to a digital control value (dec_target) suitable for the 12-bit DAC input range:

\[dec\_target = \frac{(V_{target} - 0.3V)}{2.5V} \times 4095\]

In this formula, 0.3V is the minimum voltage, 2.5V is the maximum voltage, and 4095 is the maximum value for a 12-bit DAC.

Analog pins for XMC14_2GO

On the XMC14_2GO board, pins 12 and 13 are incorrectly named

Correct mapping:
- pin 12 -> ‘A1’
- pin 13 -> ‘A0’

Correct Usage:

Use the analog pin defintions instead of 12 and 13 numbers:

analogRead(A0);  //Instead of using pin 12
analogRead(A1);  //Instead of using pin 13

I2C Analog pins

Arduino Uno R3 format dictates that A4 and A5 are also used for I2C operations, so when I2C is enabled analogue inputs A4 and A5 are NOT available.

On Arduino Uno R3 this is an alternate pin function, depending on which XMC-for-Arduino boards this could be an alternate pin function, or other case as described below.

Board	Functionality	Note
KIT_XMC11_BOOT_001	NOT supported	A4 + A5 are separate A6 + A7 are alternate pin configurations to I2C
KIT_XMC13_BOOT_001	NOT same pin format as Arduino Uno R3	A10 + A11 are alternate pin configurations to I2C
KIT_XMC1400_ARDUINO	Alternate pin function Matches Arduino Uno External hard wired pins	For 3V3 boards set I2C pins to tristate or open drain to use For 5V boards refer to this section on track cuts to enable A4 and A5 to work Level shifter on the 5V board could interfere with tristate/open drain setting
KIT_XMC47_RELAX (and variants)	External hard wired pins	For 3V3 boards set I2C pins to tristate or open drain to use For 5V boards see [this section](https://xmc-arduino.readthedocs.io/en/latest/hw-platforms.html#connected-i2s-and-analog-pins) board page on track cuts to enable A4 and A5 to work Level shifter on the 5V board could interfere with tristate/open drain setting

Serial selection

Serial Output Selection

On the XMC boards, two kinds of serial outputs are possible, namely:

SERIAL DEBUG (via PC)
SERIAL ONBOARD

If these two outputs share the same instance of the internal USIC channel, only one of the two could be used at a given time. The selection can be made via the Tools menu as shown in the picture below.

_images/arduino_ide_serial_selection.png

This is generally the case for most of the XMC boards. However, for boards such as the KIT_XMC47_RELAX, both the serial output modes are simultaneously active and need not be selected or enabled from the menu.

Note: Please note that the sketch must be recompiled when a different serial output is selected.

For advanced users The build flag -DSERIAL_HOSTPC must be used for the serial output interface via PC and the build flag -DSERIAL_ONBOARD must be used for serial output through the onboard TX and RX pins