The method using member functions has a relatively low level of abstraction and follows the general API system as provided by the C library. The procedures for operating the two-wire serial bus are more intuitive.

However, it is necessary to be explicitly aware of the start and end of bus usage.

Read

requestFrom()

size_type requestFrom(
    uint8_t u8address,
    size_type length,
    bool b_send_stop = true)

Reads the specified number of bytes at once. Since the result of reading is stored in a queue, call the .read() method immediately afterward until the queue is empty.

Code Example

int len = Wire.requestFrom(0x70, 6);
for (int i = 0; i < 6; i++) {
  if (Wire.available()) {
		  au8data[i] = Wire.read();
    Serial.print(buff[i], HEX);
  }
}
// skip the rest (just in case)
// while (Wire.available()) Wire.read(); // normally, not necessary.

Writing

Writing is performed by the write() method after executing beginTransmission(). Call endTranmission() after a series of writing is finished.

	#define DEV_ADDR (0x70)
	const uint8_t msg[2] = 
	  {SHTC3_SOFT_RST_H, SHTC3_SOFT_RST_L};

	Wire.beginTransmission(DEV_ADDR);
	Wire.write(msg, sizeof(msg));
	Wire.endTransmission();

beginTransmission()

void beginTransmission(uint8_t address)

Initialize the export transfer. Call endTransmission() as soon as the writing process is finished.

write(value)

size_type write(const value_type value)

Writes one byte.

write(*value, quantity)

size_type write(
  const value_type* value,
  size_type quantity)

Writes a byte sequence.

endTransmission()

uint8_t endTransmission(bool sendStop = true)

Processes the end of the export.

The helper class version is a more abstract implementation. Creating objects reader, writer for reading and writing is the start of using the bus, and destroying the objects is the end of using the bus.

By creating the object in the decision expression of the if statement, the validity period of the object is limited to the scope of the if clause, and the object is destroyed when it exits the if clause, at which point the bus usage termination procedure is performed.

Also, read/write objects implement the mwx::stream interface, so you can use the << operator, etc.

• Aligning the start and end of bus usage with the validity period of objects improves the visibility of source code and prevents omissions of termination procedures.

• Unification of read/write procedures by mwx::stream interface

loading

Loading process and its termination procedure in scope if() { ... } in scope.

The above reads one byte at a time using the rdr object generated by the get_readr() method. The parameter of the method is the two-line serial ID to be read. 1.

1. in if(...) Create a rdrobject in. (The type is resolved with the universal reference auto&& by type inference. 2.) The generated rdr object defines an operator bool (), which is used to evaluate the decision expression. If communication is possible with the specified ID, true is returned. 3. The rdr object defines an int operator () (void) operator, which is called to read one byte of data from the 2-wire serial bus. If the read fails, -1 is returned, and if it succeeds, the read byte value is returned. 4.

2. if() { ... } The destructor of rdr is called at the end of the scope to STOP the two-wire serial bus.

get_reader(addr, read_count=0)

I2C 読み出しに用いるワーカーオブジェクトを取得します。

write (writer)

Reading with a helper class to perform the writing process and its termination procedure in scope if() { ... } in scope.

In the above, the wrt object generated by the get_writer() method is used to write one byte at a time. The method parameter is the two-line serial ID to be read.

1. if(...) Generate a wrtobject in. (The type name is resolved with auto' because it is long. 2.) The generated wrtobject defines anoperator bool (), which is used to evaluate the decision expression. If communication is possible with the specified ID, trueis returned. 3. Thewrtobject defines anint operator () (void)operator, which is called to write one byte of data to the 2-wire serial bus. If it fails,-1` is returned, and if it succeeds, the written byte value is returned. 4.

2. if() { ... } The destructor of wrt is called at the end of the scope to STOP the two-wire serial bus.

get_writer()

Obtains the worker object used for I2C export.

Worker object (writer)

<< operator

The int and uint8_t types transfer 8 bits.

() operator

Write out 1 byte.

worker object (reader)

>> operator

Reads only the size of each data type.

() operator

Reads 1 byte. Returns -1 if there is an error, returns the byte value read if normal.

If b_stop is set to true, the STOP bit is issued on that read.

Example

The following example shows a measurement example of the temperature/humidity sensor SHTC3 of the environmental sensor PAL.

Reads and writes two-wire serial (I2C) master.

Alias Definition

using TwoWire = mwx::periph_twowire<MWX_TWOWIRE_RCVBUFF>;

The mwx::periph_wire<MWX_TWOWIRE_RCVBUFF> can be referred as TwoWire.

Type Definitions

The following definition types describe the types of arguments and return values.

typedef uint8_t size_type;
typedef uint8_t value_type;

hint style="warning %}

Initialization and termination

Wire Instance Creation

Instance creation and necessary initialization is done in the library. In user code, it is made available by calling Wire.begin().

When using the requestFrom() method, you can specify the size of the FIFO queue for temporary data storage. At compile time, compile the macro MWX_TWOWIRE_BUFF with the required number of bytes. The default is 32 bytes.

Example: -DMWX_TWOWIRE_BUFF=16

begin()

void begin(
    const size_type u8mode = WIRE_100KHZ,
    bool b_portalt = false)

Initialize hardware.

Example

void setup() {
    ...
    Wire.begin();
    ...
}

void wakeup() {
    ...
    Wire.begin();
    ...
}

Reading and Writing

There are two types of read/write procedures. Select and use one of them.

• Member function (input/output using the following member functions) requestFrom(), beginTransmission(), endTransmission(), write()

• Helper class (stream function available) reader, writer

Others

Probe（Determine presence of device)

bool probe(uint8_t address)

Checks if the device specified by address is responding. If the device exists, true is returned.

setClock()

void setClock(uint32_t speed)

The procedure is originally intended to change the bus frequency, but no action is taken.