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


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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


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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

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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





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