I2C API

To use the I2C API, begin by creating an I2C object through a call to esp32.i2cmaster,, where you specify the I2C port, SDA GPIO, SCL GPIO, and the desired I2C speed. Next, start the I2C communication sequence by calling i2cm:start, followed by i2cm:address to specify the address of the I2C device you want to communicate with. You can then proceed to call i2cm:write and/or i2c:read as needed. Finally, end the sequence by calling i2cm:commit to commit the I2C transaction.

esp32.i2cmaster

Create an I2C master object.

i2cm=esp32.i2cmaster(port, pinSDA, pinSCL, speed)

Parameters:

port (int): I2C port number - e.g. 0
pinSDA (int): the GPIO number used for the I2C Serial Data
pinSCL (int): the GPIO number used for the I2C Serial Clock
speed (int): the clock speed

I2C object methods

i2cm:start()

Start a new command sequence (new job).

i2cm:address(addr, direction, [,ack])

Add an address message to the I2C job.

Parameters:

addr (int): the slave’s I2C address

direction (string): READ or WRITE

ack (bool, optional): the I2C ack, defaults to true

i2cm:write(data [,ack])

Add a write message to the I2C job.

Parameters:

data (string): the data to write

ack (bool, optional): the I2C ack, defaults to true

i2cm:read(len [, acktype])

Read data from the I2C job.

Parameters:

len (int): how much data to read

acktype (string, optional): is one of ACK | NACK | LASTNACK, and defaults to NACK

i2cm:commit([timeout])

Commit the job and wait for a response. The default time is 500ms. Method commit returns x,err, where x is true for a successful write operation and the response data for a read operation.

I2C Example

The following example shows the read and write functions in the BME280 Lua Module. Variable regAddr is the register to read in the BME280 chip.

local function read(i2cm,regAddr,len)
   i2cm:start()
   i2cm:address(self.address, "WRITE")
   i2cm:write(regAddr)
   i2cm:start() -- Repeated Start Condition
   i2cm:address(self.address, "READ")
   i2cm:read(len)
   local x,err=i2cm:commit()
   if not x then trace("read failed",err) end
   return x,err
end

local function write(i2cm,regAddr,data)
   i2cm:start()
   i2cm:address(self.address, "WRITE")
   i2cm:write(regAddr)
   i2cm:write(data)
   local x,err=i2cm:commit()
   if not x then trace("write failed",err) end
   return x,err
end

local function bme280(port, address, sda, scl, settings)
   i2cm = esp32.i2cmaster(port, sda, scl, settings.speed or 100000)
   ......
end