CONFIG TWI

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Contents

Action

Configure the TWI (two wire serial interface).

 

 

Syntax

CONFIG TWI = clockspeed

CONFIG TWI1 = clockspeed

 

 

Syntax XMEGA

CONFIG TWIC | TWID | TWIE | TWIF = clockspeed

 

(Config TWI and TWI1 is for ATMEGA and Config TWIXis for ATXMEGA chips)

 

Remarks

clockspeed

The desired clock frequency for SCL

 

 

CONFIG TWI will set TWSR pre scaler bits 0 and 1, and TWBR depending on the used $CRYSTAL frequency and the desired SCL clock speed.

Typical you need a speed of 400 KHz. Some devices will work on 100 KHz as well.

 

When TWI is used in SLAVE mode, you need to have a faster clock speed as the master.

 

noticeThere is no dynamic channel support for I2C

noticeTo use the hardware I2C routines and not the Software I2C routines you need to use the$lib"i2c_twi.lbx"! (NOT FOR XMEGA)




Some processors support multiple TWI interfaces like the MEGA328PB. Use CONFIG TWI1 to configure the second TWI named TWI1. The first TWI which is named TWI0 is referred to as TWI.

XMEGA

The XMEGA can contain up to 4 TWI units. When not specifying TWIC, TWID, TWIE or TWIF, the TWIC will be used as  the default.

You MUST dimension a variable named TWI_START as a byte. It is used by the xmega TWI library code. Without it, you will get an error.

 

There are 2 manuals available from ATMEL for every ATXMEGA Chip

 

1. One Family Manual like for example for a ATXMEGA128A1 it is Atmel AVR XMEGA A Manual
2. Another Manual for the single chips like for example for an ATXMEGA128A1 it is the ATxmega64A1/128A1/192A1/256A1/384A1 Manual. In this Manual you find for example the Alternate Pin Functions. So you can find which Pin on Port C is the SDA and SCL Pin when you want to use the I2C/TWI Interface of this Port.

 

 

Notice.jpg
 It is important that you specify the proper crystal frequency. Otherwise it will result in a wrong TWI clock frequency.

 

 

See also

$CRYSTAL , OPEN

 

 

Example 


'-----------------------------------------------------------------------
' (c) 2004 MCS Electronics
' This demo shows an example of the TWI
' Not all AVR chips have TWI (hardware I2C)
'------------------------------------------------------------------------
 
'The chip will work in TWI/I2C master mode
'Connected is a PCF8574A 8-bits port extender
 
 
$regfile="M8def.dat"' the used chip
$crystal= 4000000 ' frequency used
$baud= 19200 ' baud rate
 
 
$lib"i2c_twi.lbx"' we do not use software emulated I2C but the TWI
 
Config Scl =Portc.5 ' we need to provide the SCL pin name
Config Sda =Portc.4 ' we need to provide the SDA pin name
 
'On the Mega8, On the PCF8574A
'scl=PC5 , pin 28 pin 14
'sda=PC4 , pin 27 pin 15
 
 
I2cinit' we need to set the pins in the proper state
 
 
Config Twi = 100000 ' wanted clock frequency
'will set TWBR and TWSR
'Twbr = 12 'bit rate register
'Twsr = 0 'pre scaler bits
 
Dim B AsByte, X AsByte
Print"TWI master"
Do
Incr B ' increase value
I2csend&B01110000 , B ' send the value
Print"Error : ";Err' show error status
I2creceive&B01110000 , X ' get a byte
Print X ;" ";Err' show error
Waitms 500 'wait a bit
Loop
End

XMEGA SAMPLE 

'----------------------------------------------------------------
' (c) 1995-2013, MCS
' xm128-TWI.bas
' This sample demonstrates the Xmega128A1 TWI
'-----------------------------------------------------------------
 
$regfile = "xm128a1def.dat"
$crystal = 32000000
$hwstack = 64
$swstack = 40
$framesize = 40
 
 
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 Twic = 100000 'CONFIG TWI will ENABLE the TWI master interface
'you can also use TWIC, TWID, TWIE of TWIF
'!!!!!!!!!!! WITHOUT a channel identifier, TWIC will be used !!!!!!!!!!!!!!
 
#if Usechannel = 1
I2cinit #4
#else
I2cinit
#endif
 
 
Do
I2cstart 'since not # is used, TWIC will be used
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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