I2CSTART

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 this 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.

 

All I2C statements are master mode statements. They will code from the i2c.lib. There is also an improved version of this library available named i2cv2.lib

Since the repeated start is not compatible with the one from i2c.lib, you need to specify yourself that you want to use the improved lib. See also I2CV2.

I2CSTOP and Xmega

The I2CSTOP statement on the Xmega can be influenced by defining a constant named _TWI_STOP_NEW

The value does not matter. So you can add :  CONST _TWI_STOP_NEW = 1

This code will use the preferred code to generate an I2CSTOP command. Why this option? Some Xmega do not respond well to a command to free the bus. As a work around , multiple commands are given till the bus is free.

Some slave chips might have a problem with that. For this reason, the DEFAULT is the old way to send multiple STOP commands till the bus is free.

By defining the _TWI_STOP_NEW constant, you can use the new, preferred method which will give a STOP command and then poll the status till the bus is actually free. Since not all Xmega respond well to this, this is made an option.

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 , I2CSTOP, I2CRBYTE , I2CWBYTE , I2CV2

 

 

Example (using Software I2C Routines)

'-----------------------------------------------------------------------------------------
'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

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