SMBus Library

The SMBus I/O interface is a two-wire, bi-directional serial bus. The System Management Bus is compatible with the I2C serial bus.

SMBus module is available with a number of Silicon Laboratories 8051 MCU models. mikroBasic PRO for 8051 provides library which supports the master SMBus mode.

SMBus1_Init

Prototype	sub procedure SMBus1_Init(dim clock as longword)
Returns	Nothing.
Description	Initializes SMBus with desired `clock` (refer to device datasheet for correct values in respect with Fosc). Needs to be called before using other functions of SMBus Library.
Requires	Library requires SMBus module.
Example	SMBus1_Init(100000)

SMBus1_Start

Prototype	sub function SMBus1_Start() as byte
Returns	If there is no error function returns 0, otherwise returns 1.
Description	Determines if SMBus bus is free and issues START signal.
Requires	SMBus must be configured before using this function. See SMBus1_Init.
Example	if (SMBus1_Start = 1) begin ... end.

SMBus1_Repeated_Start

Prototype	sub function SMBus1_Repeated_Start() as byte
Returns	If there is no error function returns 0, otherwise returns 1.
Description	Issues repeated START signal.
Requires	SMBus must be configured before using this function. See SMBus1_Init.
Example	SMBus1_Repeated_Start()

SMBus1_Busy

Prototype	sub function SMBus1_Busy() as byte
Returns	Returns 0 if SMBus start sequence is finished, 1 if SMBus start sequence is not finished.
Description	Signalizes the status of SMBus bus.
Requires	SMBus must be configured before using this function. See SMBus1_Init.
Example	if (SMBus1_Busy = 1) begin ... end.

SMBus1_Read

Prototype	sub function SMBus1_Read(dim nack_ as byte) as byte
Returns	Returns one byte from the slave.
Description	Reads one byte from the slave, and sends acknowledge signal if parameter `nack` is 1, otherwise it sends not acknowledge.
Requires	SMBus must be configured before using this function. See SMBus1_Init. Also, START signal needs to be issued in order to use this function. See SMBus1_Start.
Example	Read data and send not acknowledge signal: tmp = SMBus1_Read(0)

SMBus1_Write

Prototype	sub procedure SMBus1_Write(dim data_ as byte)
Returns	Nothing.
Description	Sends data byte (parameter `data_`) via SMBus bus.
Requires	SMBus must be configured before using this function. See SMBus1_Init. Also, START signal needs to be issued in order to use this function. See SMBus1_Start.
Example	SMBus1_Write(0xA3)

SMBus1_Status

Prototype	sub function SMBus1_Status() as byte
Returns	Returns value of status register.
Description	Returns status of SMBus.
Requires	SMBus must be configured before using this function. See SMBus1_Init.
Example	status = SMBus1_Status()

SMBus1_Stop

Prototype	sub procedure SMBus1_Stop()
Returns	Nothing.
Description	Issues STOP signal to SMBus operation.
Requires	SMBus must be configured before using this function. See SMBus1_Init.
Example	SMBus1_Stop()

SMBus1_Close

Prototype	sub procedure SMBus1_Close()
Returns	Nothing.
Description	Closes SMBus connection.
Requires	SMBus must be configured before using this function. See SMBus1_Init.
Example	SMBus1_Close()

Library Example

This code demonstrates use of SMBus Library sub 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 SMBus from EEPROM and send its value to PORTA, to check if the cycle was successful. Check the figure below.

program I2C_Simple

dim ee_data as byte

main:
  WDTCN    = 0xDE                      ' Sequence for
  WDTCN    = 0xAD                      '   disabling the watchdog timer
  OSCICN   = 0x83                      ' Enable internal oscillator (24.5MHz divided by 1)
  P0MDOUT  = P0MDOUT or %00001101      ' Configure P0.3(SCK), P0.2(SDA)
                                       '   and P0.0(TX) pin as push-pull

  UART1_Init(4800)                     ' Initialize UART module at 4800 bps
  Delay_ms(100)                        ' Wait for UART module to stabilize
  UART1_Write_Text("Start ")

  SMBus1_Init(32000)                   ' initialize I2C communication
  SMBus1_Start()                       ' issue I2C start signal
  SMBus1_Write(0xA2)                   ' send byte via I2C  (device address + W)
  SMBus1_Write(2)                      ' send byte (address of EEPROM location)
  SMBus1_Write(0xFF)                   ' send data (data to be written)
  SMBus1_Stop()                        ' issue I2C stop signal

  Delay_100ms()

  SMBus1_Start()                       ' issue I2C start signal
  SMBus1_Write(0xA2)                   ' send byte via I2C  (device address + W)
  SMBus1_Write(2)                      ' send byte (data address)
  SMBus1_Repeated_Start()              ' issue I2C signal repeated start
  SMBus1_Write(0xA3)                   ' send byte (device address + R)
  ee_data = SMBus1_Read(0)             ' Read the data (NO acknowledge)
  UART1_Write(ee_data)
  SMBus1_Stop()                        ' issue I2C stop signal
end.
end.

HW Connection

Interfacing 24c02 to 8051 via SMBus

Want more examples and libraries?
Find them on