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I2C

  • A class that supports I2C bus.
  • This specification supports only master devices with 7-bit addresses.
  • Define two types of methods: convenience methods, which are easy to use, and low-level methods, which provide detailed control.
  • The low-level methods should be implemented on an as-needed basis, since it is unlikely that they will be needed in most cases.

Constructor

I2C.new( id=nil, *params )

  • Generates an I2C object by specifying the physical unit indicated by "id."
  • "id" can be omitted when there is only one physical unit.

Optional Parameters

param type description
frequency Integer Frequency (default 100kHz)
freq (Same as above)
scl_pin --- SCL pin specification
sda_pin --- SDA pin specification

Example of use:

# Generate an I2C object with the default settings.
i2c = I2C.new()

# Use an I2C device of unit 1 with a frequency of 400kHz.
i2c = I2C.new(1, frequency:400_000 )   # 400kHz

Device-specific

  • Not all parameters may be supported.

Instance Methods

read( i2c_adrs_7, read_bytes, *param ) -> String

  • Reads data of read_bytes bytes from the device with the address i2c_adrs_7.
  • If the device returns NAK in the middle, a String of shorter length than read_bytes may be returned.
  • If data is specified in the param, it will be output before the repeated start, and then reading will start.
  • Output specifications are the same as for write().

Example of use:

s = i2c.read( 0x45, 3 )                 # case 1
s = i2c.read( 0x45, 3, 0xf3, 0x2d )     # case 2

I2C bus sequence

(case 1) S -- adrs(45) R A -- data1 A -- data2 A -- data3 A|N -- P
(case 2) S -- adrs(45) W A -- out1(f3) A -- out2(2d) A -- Sr -- adrs(45) R A -- data1 A -- data2 A -- data3 N -- P
    S : Start condition
    P : Stop condition
    Sr: Repeated start condition
    A : Ack
    N : Nack
    R : Read bit
    W : Write bit

write( i2c_adrs_7 , *outputs ) -> Integer

  • Writes data specified in outputs to the device with the address i2c_adrs_7.
  • The number of bytes successfully written is returned as the return value.
  • outputs can be specified as an Integer, Array, or String.

Example of use:

i2c.write( 0x45, 0x30, 0xa2 )
i2c.write( 0x50, 0x00, 0x80, data_string )  # useful for EEPROM
i2c.write( 0x11, [0x30, 0xa2] )

I2C Sequence

S -- adrs W A -- data_1 A -- ... -- data_n N -- P
    S : Start condition
    P : Stop condition
    A : Ack
    N : Nack
    W : Write bit

send_start()

  • Low level method.
  • Outputs a StartCondition to the I2C bus.

Example of use:

i2c.send_start

send_restart()

  • Low level method.
  • Outputs a Restart (RepeatedStart) Condition to the I2C bus.

Example of use:

i2c.send_restart

send_stop()

  • Low level method.
  • Outputs a StopCondition to the I2C bus.

Example of use:

i2c.send_stop

raw_read( read_bytes, ack_nack = false ) -> String

  • Low level method.
  • Reads read_bytes bytes from the I2C bus and returns them.
  • ack_nack = true outputs ACK at the last byte reading, and false outputs NACK.

Example of use:

str = i2c.raw_read( 20 )

raw_write( *outputs ) -> Integer

  • Low level method.
  • Writes data specified in outputs to the I2C bus.
  • The number of bytes successfully written is returned as the return value.
  • outputs can be specified as an Integer, Array, or String.

Example of use:

i2c.raw_write( 0x45, 0x30, 0xa2 )