Hardware abstraction layer (HAL) for communicating over TWI/I2C with the display. Basic settings like the speed of the bus and pins can be defined in twi_soft.h.
Software-defined TWI makes communication more flexible because the ports can be switched.
TWI-Bus speed definition
The TWI transmission speed can be set up within the F_SOFT_TWI macro (100 kHz is set by default).
#define F_SOFT_TWI 100000UL
Internal/External pull-up resistors
The software-twi bus can either be run with external or with internal pull-up resistors. The internal pull-up resistors can be enabled with the TWI_SOFT_PULLUP_ENABLE macro (not enabled by default).
#define TWI_SOFT_PULLUP_ENABLE
The internal pull-up resistors depend on the microcontroller and have a wide range. Therefore, low bus transfer rates should be selected without measuring with an oscilloscope.
Pin definition of TWI-SCL/SDA
The advantage of the software TWI bus is that the pins for SCL and SDA can be freely selected. They just have to be in the same register. Therefore it is necessary to define the whole bunch of registers and pins.
// Register set for SCL/SDA pins
#define TWI_SOFT_DDR DDRB
#define TWI_SOFT_PORT PORTB
#define TWI_SOFT_PIN PINB
// SCL/SDA pins
#define TWI_SOFT_SCL PINB0
#define TWI_SOFT_SDA PINB1
Interrupt blocking during transmission
If a transmission should not be interrupted, the software TWI library can be stopped to block interrupts during transmissions (not enabled by default).
If enabled, no interrupt will be processed until the transfer is complete!
#define TWI_SOFT_BLOCK_IE
For a more detailed view of the possible parameters that can be set in twi_soft.h, take a look at the OLED Doxygen documentation (OLDD).