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Bit Bang I2C library

Copyright (c) 2018 BitBank Software, Inc. Written by Larry Bank (bitbank@pobox.com) Project started 10/12/2018

The purpose of this code is to provide a simple C library which can manage I2c in a consistent way across different platforms, in addition to providing software bit-bang of the protocol on any 2 GPIO pins. The I2C protocol doesn't require any special functionality of the pins beyond standard GPIO features. The reason I wrote it was for getting easy access to I2C devices on various microcontrollers that don't necessarily have exposed I2C interfaces. This has come in handy on a variety of projects including AVR, ESP32, and nRF5 micrcontrollers.

The pin access functions can be wrapper functions for the native versions (e.g. on the nRF5 SDK) On AVR micros, the digitalWrite/digitalRead/pinMode functions are somewhat slow because they check the pin numbers against tables and do other tasks. This library includes logic to speed that up. By specifying pin numbers as the port name + bit, the library will run considerably faster on AVR microcontrollers. For example, On the Arduino Uno (ATmega328P), I/O pin 9 is actually I/O Port B, bit 1. To use the direct pin method, you would specify the pin number as 0xB1. On the ATtiny85, this is the only pin numbering supported so that the Wire library doesn't get linked in (to save FLASH space).

This latest version allows you to use this library for both bit-bang I2C or make use of the Wire library indirectly. Since each BBI2C object is independent, you can have as many buses as you like operating on any combination of bit-bang and hardware I2C.

Usage:

Start by initializing a BBI2C structure with the desired pin numbers for SDA/SCL along with the desired clock frequency. The bWire flag tells the library to use hardware I2C when set to true. If using the hardware I2C (Wire library), the pin numbers can be set to 0xff to use the default I2C pins or to specific pins on systems which support multiple I2C buses. Frequencies above 400Khz are possible, but not necessarily accurate. Luckily I2C devices don't really care about the exact clock frequency, only that the signals are stable within the given periods.

For Example:

BBI2C bbi2c;
bbi2c.bWire = 0; // use bit banging
bbi2c.iSDA = 10; // SDA on GPIO pin 10
bbi2c.iSCL = 11; // SCL on GPIO pin 11
I2CInit(&bbi2c, 100000); // SDA=pin 10, SCL=pin 11, 100K clock

Instead of exposing functions to start and stop I2C transactions, I decided to make it simpler by providing composite functions that hide the details of I2C protocol. For scanning the I2C bus for devices, I provide the I2CScan() function which returns a bitmap (16 bytes x 8 bits) with a bit set for every device it finds. Call it like this:

unsigned char ucMap[16];
I2CScan(&bbi2c, ucMap);

To detect if a single address is active, use I2CTest(addr).

To identify the device, use I2CDiscoverDevice(uint8_t iAddress).

For reading and writing data to the I2C device, use the following functions:

I2CRead(&bbi2c, uint8_t u8Address, uint8_t *pu8Data, int iLength);
I2CReadRegister(&bbi2c, uint8_t iAddr, uint8_t u8Register, uint8_t *pData, int iLen);
I2CWrite(&bbi2c, uint8_t iAddr, uint8_t *pData, int iLen);

There are currently 43 devices recognized by the discover function:

  • SSD1306
  • SH1106
  • VL53L0X
  • BMP180
  • BMP280
  • BME280
  • BME680
  • MPU6000
  • MPU9250
  • MCP9808
  • LSM6DS3
  • ADXL345
  • ADS1115
  • MAX44009
  • MAG3110
  • CCS811
  • HTS221
  • LPS25H
  • LSM9DS1
  • LM8330
  • DS3231
  • DS1307
  • LIS3DH
  • LIS3DSH
  • INA219
  • SHT3X
  • HDC1080
  • AXP192
  • AXP202
  • 24AAXXXE64
  • DS1307
  • MPU688X
  • FT6236G
  • FT6336G
  • FT6336U
  • FT6436
  • BM8563
  • BNO055
  • AHT20
  • TMF882X
  • SCD4X
  • ST25DV
  • LTR390
  • BMP388

If you find this code useful, please consider sending a donation.

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