Action
I2CSTART generates an I2C start condition.
I2CREPSTART generates an I2C repeated start condition.
I2CSTOP generates an I2C stop condition.
I2CRBYTE receives one byte from an I2C-device.
I2CWBYTE sends one byte to an I2C-device.
Syntax
I2CSTART
I2CREPSTART
I2CSTOP
I2CRBYTE var, ack/nack
I2CWBYTE val
Syntax Xmega
I2CSTART #const
I2CREPSTART #const
I2CSTOP #const
I2CRBYTE var, ack/nack , #const
I2CWBYTE val , #const
Remarks
Var |
A variable that receives the value from the I2C-device. |
ack/nack |
Specify ACK if there are more bytes to read.
Specify NACK if it is the last byte to read. |
Val |
A variable or constant to write to the I2C-device. |
#const |
For the Xmega, a channel constant that was specified with OPEN. |
These statements are provided as an addition to the I2CSEND and I2CRECEIVE statements.
While I2CSEND and I2CRECEIVE are well suited for most tasks, a slave chip might need a special sequence that is not possible with the I2C routines.
When an error occurs, the internal ERR variable will return 1. Otherwise it will be set to 0.
The Xmega has multiple TWI interfaces. You can use a channel to specify the TWI interface.
When using a repeated start, you must use I2CREPSTART on the XMega.
Normal AVR processors may use either I2CSTART or I2CREPSTART.
ASM
The I2C routines are located in the i2c.lib/i2c.lbx files.
For the XMega, the routines are located in the xmega.lib file.
See also
I2CSEND , I2CRECEIVE , I2CSTART , I2CSTOP, I2CRBYTE , I2CWBYTE
Example
'-----------------------------------------------------------------------------------------
'name : i2c.bas
'copyright : (c) 1995-2005, MCS Electronics
'purpose : demo: I2CSEND and I2CRECEIVE
'micro : Mega48
'suited for demo : yes
'commercial addon needed : no
'-----------------------------------------------------------------------------------------
$regfile = "m48def.dat" ' specify the used micro
$crystal = 4000000 ' used crystal frequency
$baud = 19200 ' use baud rate
$hwstack = 32 ' default use 32 for the hardware stack
$swstack = 10 ' default use 10 for the SW stack
$framesize = 40 ' default use 40 for the frame space
Config Scl = Portb.4
Config Sda = Portb.5
Declare Sub Write_eeprom(byval Adres As Byte , Byval Value As Byte)
Declare Sub Read_eeprom(byval Adres As Byte , Value As Byte)
Const Addressw = 174 'slave write address
Const Addressr = 175 'slave read address
Dim B1 As Byte , Adres As Byte , Value As Byte 'dim byte
Call Write_eeprom(1 , 3) 'write value of three to address 1 of EEPROM
Call Read_eeprom(1 , Value) : Print Value 'read it back
Call Read_eeprom(5 , Value) : Print Value 'again for address 5
'-------- now write to a PCF8474 I/O expander -------
I2csend &H40 , 255 'all outputs high
I2creceive &H40 , B1 'retrieve input
Print "Received data " ; B1 'print it
End
Rem Note That The Slaveaddress Is Adjusted Automaticly With I2csend & I2creceive
Rem This Means You Can Specify The Baseaddress Of The Chip.
'sample of writing a byte to EEPROM AT2404
Sub Write_eeprom(byval Adres As Byte , Byval Value As Byte)
I2cstart 'start condition
I2cwbyte Addressw 'slave address
I2cwbyte Adres 'asdress of EEPROM
I2cwbyte Value 'value to write
I2cstop 'stop condition
Waitms 10 'wait for 10 milliseconds
End Sub
'sample of reading a byte from EEPROM AT2404
Sub Read_eeprom(byval Adres As Byte , Value As Byte)
I2cstart 'generate start
I2cwbyte Addressw 'slave adsress
I2cwbyte Adres 'address of EEPROM
I2cstart 'repeated start
I2cwbyte Addressr 'slave address (read)
I2crbyte Value , Nack 'read byte
I2cstop 'generate stop
End Sub
' when you want to control a chip with a larger memory like the 24c64 it requires an additional byte
' to be sent (consult the datasheet):
' Wires from the I2C address that are not connected will default to 0 in most cases!
' I2cstart 'start condition
' I2cwbyte &B1010_0000 'slave address
' I2cwbyte H 'high address
' I2cwbyte L 'low address
' I2cwbyte Value 'value to write
' I2cstop 'stop condition
' Waitms 10
Xmega Example
'----------------------------------------------------------------
' (c) 1995-2010, MCS
' xm128-TWI.bas
' This sample demonstrates the Xmega128A1 TWI
'-----------------------------------------------------------------
$regfile = "xm128a1def.dat"
$crystal = 32000000
$hwstack = 64
$swstack = 40
$framesize = 40
'include the following lib and code, the routines will be replaced since they are a workaround
$lib "xmega.lib"
$external _xmegafix_clear
$external _xmegafix_rol_r1014
Dim S As String * 20
'first enable the osc of your choice
Config Osc = Enabled , 32mhzosc = Enabled
'configure the systemclock
Config Sysclock = 32mhz , Prescalea = 1 , Prescalebc = 1_1
Dim N As String * 16 , B As Byte
Config Com1 = 19200 , Mode = Asynchroneous , Parity = None , Stopbits = 1 , Databits = 8
Config Input1 = Cr , Echo = Crlf ' CR is used for input, we echo back CR and LF
Open "COM1:" For Binary As #1
' ^^^^ change from COM1-COM8
Print #1 , "Xmega revision:" ; Mcu_revid ' make sure it is 7 or higher !!! lower revs have many flaws
Const Usechannel = 1
Dim B1 As Byte , B2 As Byte
Dim W As Word At B1 Overlay
Open "twic" For Binary As #4 ' or use TWID,TWIE oR TWIF
Config Twi = 100000 'CONFIG TWI will ENABLE the TWI master interface
'you can also use TWIC, TWID, TWIE of TWIF
#if Usechannel = 1
I2cinit #4
#else
I2cinit
#endif
Do
I2cstart
Waitms 20
I2cwbyte &H70 ' slave address write
Waitms 20
I2cwbyte &B10101010 ' write command
Waitms 20
I2cwbyte 2
Waitms 20
I2cstop
Print "Error : " ; Err ' show error status
'waitms 50
Print "start"
I2cstart
Print "Error : " ; Err ' show error
I2cwbyte &H71
Print "Error : " ; Err ' show error
I2crbyte B1 , Ack
Print "Error : " ; Err ' show error
I2crbyte B2 , Nack
Print "Error : " ; Err ' show error
I2cstop
Print "received A/D : " ; W ; "-" ; B1 ; "-" ; B2
Waitms 500 'wait a bit
Loop
Dim J As Byte , C As Byte , K As Byte
Dim Twi_start As Byte ' you MUST dim this variable since it is used by the lib
'determine if we have an i2c slave on the bus
For J = 0 To 200 Step 2
Print J
#if Usechannel = 1
I2cstart #4
#else
I2cstart
#endif
I2cwbyte J
If Err = 0 Then ' no errors
Print "FOUND : " ; Hex(j)
'write some value to the pcf8574A
#if Usechannel = 1
I2cwbyte &B1100_0101 , #4
#else
I2cwbyte &B1100_0101
#endif
Print Err
Exit For
End If
#if Usechannel = 1
I2cstop #4
#else
I2cstop
#endif
Next
#if Usechannel = 1
I2cstop #4
#else
I2cstop
#endif
#if Usechannel = 1
I2cstart #4
I2cwbyte &H71 , #4 'read address
I2crbyte J , Ack , #4
Print Bin(j) ; " err:" ; Err
I2crbyte J , Ack , #4
Print Bin(j) ; " err:" ; Err
I2crbyte J , Nack , #4
Print Bin(j) ; " err:" ; Err
I2cstop #4
#else
I2cstart
I2cwbyte &H71 'read address
I2crbyte J , Ack
Print Bin(j) ; " err:" ; Err
I2crbyte J , Ack
Print Bin(j) ; " err:" ; Err
I2crbyte J , Nack
Print Bin(j) ; " err:" ; Err
I2cstop
#endif
'try a transaction
#if Usechannel = 1
I2csend &H70 , 255 , #4 ' all 1
Waitms 1000
I2csend &H70 , 0 , #4 'all 0
#else
I2csend &H70 , 255
Waitms 1000
I2csend &H70 , 0
#endif
Print Err
'read transaction
Dim Var As Byte
Var = &B11111111
#if Usechannel = 1
I2creceive &H70 , Var , 1 , 1 , #4 ' send and receive
Print Bin(var) ; "-" ; Err
I2creceive &H70 , Var , 0 , 1 , #4 ' just receive
Print Bin(var) ; "-" ; Err
#else
I2creceive &H70 , Var , 1 , 1 ' send and receive
Print Bin(var) ; "-" ; Err
I2creceive &H70 , Var , 0 , 1 ' just receive
Print Bin(var) ; "-" ; Err
#endif
End