3.3Kohm would be ok... maybe even bigger. The most common value is 4.7K but you
can reduce it. The important factor is the capacitance in the lines. If the
devices are close to each other you can increase the pull-up.
You have to think that the system speed is regarding your maximum allowed rise
or fall time. If your clock is 125KHz the rise and fall time can be around 0.5us
and you would still be ok. This means 2MHz for I2C system frequency. Then the RC
formed by pull-up and traces/pins/circuit board/etc total capacitance shall
result in less than 0.5us. With 10Kohm the capacitance shall be less than 50pF.
If it is the case you can use 10Kohm pull-up. With 3K3 you can have up to 150pF.
The limit is the drive strength of MSP430's output pin. With 3K3 you will
have around 1mA.
-Augusto
De:m...
Para:m...
Cia:
Data:Wed, 25 Mar 2009 17:06:36 -0300
Assunto:[msp430] Re: pull up I2C
fix:
the frequency is 125KHz
2009/3/25 Edson Burgo
> Hi, i would know what the value of resistor i need
use on the bus I2C (pull
> up) to make comunication between MSP430F2013 and EEPROM (24LC08) with 125
> Hz.
> Or can i use intern resistor ???
>
> thanks since now.
>
> Edson
>
--
Edson Luiz Burgo Jior
CAEL (Centro Acadico de Engenharia Elrica)
MSN: e...@hotmail.com
Cel: (43) 9906-1832