TWI Library

TWI full master MSSP module is available with a number of 8051 MCU models. mikroBasic PRO for 8051 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	sub procedure TWI_Init(dim clock as longword)
Returns	Nothing.
Description	Initializes TWI with desired `clock` (refer to device datasheet 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.
Requires	Library requires MSSP module on PORTB or PORTC.
Example	TWI_Init(100000)

TWI_Busy

Prototype	sub function TWI_Busy() as byte
Returns	Returns 0 if TWI start sequnce is finished, 1 if TWI start sequnce is not finished.
Description	Signalizes the status of TWI bus.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	if (TWI_Busy = 1) ... end if

TWI_Start

Prototype	sub function TWI_Start() as byte
Returns	If there is no error function returns 0, otherwise returns 1.
Description	Determines if TWI bus is free and issues START signal.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	if (TWI_Start = 1) ... end if

TWI_Read

Prototype	sub function TWI_Read(dim ack as byte) as 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.
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	sub procedure TWI_Write(dim data_ as byte)
Returns	Nothing.
Description	Sends data byte (parameter `data_`) via TWI bus.
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	sub procedure TWI_Stop()
Returns	Nothing.
Description	Issues STOP signal to TWI operation.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	TWI_Stop()

TWI_Status

Prototype	sub function TWI_Status() as byte
Returns	Returns value of status register (TWSR), the highest 5 bits.
Description	Returns status of TWI.
Requires	TWI must be configured before using this function. See TWI_Init.
Example	status = TWI_Status()

TWI_Close

Prototype	sub procedure TWI_Close()
Returns	Nothing.
Description	Closes TWI connection.
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. 8051 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.

program TWI_Simple

main:
  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)
  P0 = TWI_Read(0)         ' read data (NO acknowledge)
  TWI_Stop()               ' issue TWI stop signal}
end.

HW Connection

Interfacing 24c02 to 8051 via TWI

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