Attiny85 USI TWI/I2C examples

• Attiny USI TWI/I2C simple examples and PCF8574 GPIO expander.
• Very small compared to Arduino version because its directly coded using the RISC Instruction Set MCU Registers.

Tools

1. Software

• AVRDdude Programmer
• AVR-GCC
• Linux OpenSuSE Tumbleweed
• Nick Gammon SendOnlySoftwareSerial Library (https://github.com/nickgammon/SendOnlySoftwareSerial)

2. Hardware

• USBASP
• Attiny85
• PCF8574
• Keypad 4x4 Membrane Matrix
• CP2102 USB to TTL/Serial (for debugging)

Connection

1. Connect Attiny pins to PCF8574 I2C pins
2. Connect Keypad pins to PCF8574 IO pins
3. Connect CP2102 to Attiny85 pin.

Build

• You might one to check the Makefile first before running make.
• And run make and make flash

affan@tumbleweed:~/uC/tiny85/c/T85-USI-PCF8574> make
avr-gcc -std=c99 -Wall -g -Os -mmcu=attiny85 -DF_CPU=1000000 -I.  -o main.o main.c
/usr/lib64/gcc/avr/11/ld: warning: -z relro ignored
avr-objcopy -j .text -j .data -O ihex main.o main.hex
avr-size -C --mcu=attiny85 main.o
AVR Memory Usage
----------------
Device: attiny85

Program:     372 bytes (4.5% Full)
(.text + .data + .bootloader)

Data:          3 bytes (0.6% Full)
(.data + .bss + .noinit)