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Created page with "= Action = Configure the TWI (two wire serial interface). &n..."

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== (**COPIED FROM ENGLISH PAGE**) === Action =

Configure the TWI (two wire serial interface).

 

 

= Syntax =

CONFIG TWI = clockspeed

CONFIG TWIC | TWID | TWIE | TWIF = clockspeed

 

(Config TWI is for ATMEGA and Config TWIX is for ATXMEGA chips)

 

= Remarks =
<div style="padding: 0px; margin: 0px 0px 0px 4px;">
{| width="485" cellspacing="0" cellpadding="1" border="1" style="border: 2px solid rgb(0, 0, 0); border-spacing: 0px; border-collapse: collapse;"
|- style="vertical-align: top;"
| valign="top" width="24%" style="width: 112px; border: 1px solid rgb(0, 0, 0);" |
clockspeed

| valign="top" width="100%" style="width: 364px; border: 1px solid rgb(0, 0, 0);" |
The desired clock frequency for SCL

|}
</div>
 

 

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.

 

= 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

 
<div style="padding: 0px; margin: 0px;">
{| border="0" cellpadding="0" cellspacing="0"
|- valign="baseline" style="vertical-align: baseline;"
| width="15" | 1.
| One Family Manual like for example for a ATXMEGA128A1 it is Atmel AVR XMEGA A Manual
|}
</div><div style="padding: 0px; margin: 0px;">
{| border="0" cellpadding="0" cellspacing="0"
|- valign="baseline" style="vertical-align: baseline;"
| width="15" | 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.
|}
</div>
 

 

[[File:Notice.jpg|left|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 =

 <source lang="bascomavr">
'-----------------------------------------------------------------------
' (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
</source> {{Languages}}

[[Category:BASCOM Language Reference/de]]

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