TWI Library

TWI full master MSSP module is available with a number of AVR MCU models. mikroPascal PRO for AVR provides library which supports the master TWI mode.

Library Routines

TWI_Init
TWI_Busy
TWI_Start
TWI_Stop
TWI_Read
TWI_Write
TWI_Status
TWI_Close

TWI_Init

Prototype	procedure TWI_Init(clock : dword); // for XMEGA family of MCUs procedure TWIx_Init(clock : dword);
Returns	Nothing.
Description	Initializes TWI with desired `clock` (refer to device data sheet for correct values in respect with Fosc). Needs to be called before using other functions of TWI Library. You don’t need to configure ports manually for using the module; library will take care of the initialization. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	Library requires MCU with TWI module.
Example	TWI_Init(100000);

TWI_Busy

Prototype	function TWI_Busy() : byte; // for XMEGA family of MCUs function TWIx_Busy() : byte;
Returns	`0` - if TWI bus is not busy `1` - if TWI bus is busy
Description	Signalizes the status of TWI bus. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	if (TWI_Busy = 0) begin ... end;

TWI_Start

Prototype	function TWI_Start() : char; // for XMEGA family of MCUs function TWIx_Start() : char;
Returns	`0` - if TWI start sequence is finished `1` - if TWI start sequence is not finished
Description	Determines if TWI bus is free and issues START signal. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	if (TWI_Start = 0) begin ... end;

TWI_Read

Prototype	function TWI_Read(ack : byte) : byte; // for XMEGA family of MCUs function TWIx_Read(ack : byte) : byte;
Returns	Returns one byte from the slave.
Description	Reads one byte from the slave, and sends not acknowledge signal if parameter `ack` is 0, otherwise it sends acknowledge. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init. Also, START signal needs to be issued in order to use this function. See TWI_Start.
Example	Read data and send not acknowledge signal: tmp := TWI_Read(0);

TWI_Write

Prototype	procedure TWI_Write(data_ : byte); // for XMEGA family of MCUs procedure TWIx_Write(data_ : byte);
Returns	Nothing.
Description	Sends data byte (parameter `data_`) via TWI bus. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init. Also, START signal needs to be issued in order to use this function. See TWI_Start.
Example	TWI_Write(0xA3);

TWI_Stop

Prototype	procedure TWI_Stop(); // for XMEGA family of MCUs procedure TWIx_Stop();
Returns	Nothing.
Description	Issues STOP signal to TWI operation. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	TWI_Stop();

TWI_Status

Prototype	function TWI_Status() : byte; // for XMEGA family of MCUs function TWIx_Status() : byte;
Returns	Returns value of status register (TWSR), the highest 5 bits.
Description	Returns status of TWI. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	status := TWI_Status();

TWI_Close

Prototype	procedure TWI_Close(); // for XMEGA family of MCUs procedure TWIx_Close();
Returns	Nothing.
Description	Closes TWI connection. For XMEGA family of MCUs change the X in the routine prototype with C, D, E or F.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	TWI_Close();

Library Example

This code demonstrates use of TWI Library procedures and functions. AVR MCU is connected (SCL, SDA pins ) to 24c02 EEPROM. Program sends data to EEPROM (data is written at address 2). Then, we read data via TWI from EEPROM and send its value to PORTA, to check if the cycle was successful. Check the figure below.

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program TWI_Simple;

begin
  DDRA := 0xFF;             // configure PORTA as output

  TWI_Init(100000);         // initialize TWI communication
  TWI_Start();              // issue TWI start signal
  TWI_Write(0xA2);          // send byte via TWI (device address + W)
  TWI_Write(2);             // send byte (address of EEPROM location)
  TWI_Write(0xAA);          // send data (data to be written)
  TWI_Stop();               // issue TWI stop signal

  Delay_100ms();

  TWI_Start();              // issue TWI start signal
  TWI_Write(0xA2);          // send byte via TWI (device address + W)
  TWI_Write(2);             // send byte (data address)
  TWI_Start();              // issue TWI signal repeated start
  TWI_Write(0xA3);          // send byte (device address + R)
  PORTA := TWI_Read(0);     // read data (NO acknowledge)
  TWI_Stop();               // issue TWI stop signal}
end.

HW Connection

Interfacing 24c02 to AVR via I²C

Interfacing 24c02 to AVR via TWI

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