I2C pullup resistors needed?

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Kentxu
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I2C pullup resistors needed?

Hello,

I noticed that the resistors R2 and R3 I2C pullup are not mounted on the SLG46826V-DIP board.

There is no option in the GreenPAK6 software to enable pullups on the I2C pins. Also, pullups are included on the GreenPAK In-System Programming Board. But I am wondering what happens to these pins when the SLG46826 chip is running stand alone. ie. will they be susceptible to noise?

So my question is do I need to include I2C pullup resistors on my board for the SLG46826?

Thanks, Ken

Device: 
Device Number: 
SLG46826
olehs
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Joined: 2018-02-07 11:40
Hi Kentxu, 

Hi Kentxu, 

Thank you for your question!

If you are using GreenPAK DIP Development Board, it has the possibility to add the external onboard 5kOhm Pull Up (or Pull Down) resistors. To add them please start the Debug Mode and you will be able to add the externally connected resistors. For the I2C line they are added by default. Please see the attached file I made a screenshot. I hope, it will help you to solve your problem.

The resistors R2 and R3 you mentioned, these resistors will not affect any functionality of the board and I2C itself.

Best regards, 

Oleh Sapiha

Attachment: 
Kentxu
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Last seen: 1 year 11 months ago
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Hi Oleh,

Hi Oleh,

Thanks for the reply. But I am not using the DIP Development Board.

I am designing a new board which includes the SLG46826 and there is not much room, so I want to know if the I2C pullup resistors are needed on my board.

Thanks, Ken

olehs
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Kentxu, 

Kentxu, 

Sorry for my misunderstanding, if you are using I2C line, PINs should be externally pulled up either from the Master Side or from the Slave side (SLG46826V). If you have pull up resistors from the master side, you don't need to add additional resistors. Otherwise, pull up resistors should be added.

Best regards,

Oleh Sapiha

Kentxu
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Last seen: 1 year 11 months ago
Joined: 2019-12-19 00:31
Hi Oleh,

Hi Oleh,

Thanks for the clarification. Once it is ISP programmed my SLG46826V chip will be running 'stand alone' (no master) so I will add some pullups.

It would have been good if the I2C pullups were inside the chip by default, oh well. :(

Perhaps a recommended circuit diagram with minimum needed components (pullups, decoupling) would be good to have in the data sheet.

BR, Ken

olehs
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Kentxu, 

Kentxu, 

Inside the chip pull up resistor create the limitation, since the I2C master can have a differed VDD range supply and this will be not good for communication and chip operating. There are pull up resistors 10kOhm on other nearby PINs, for example, PIN7, and PIN10 can be externally connected with PIN8 and PIN9 accordingly. This approach will let you pull up the I2C PINs without additional components and save the space on your PCB, but nearby PINs must not be used in your design.  

The external components are like Pull Up resistors are not permanent and can be changed depending on the line capacitance and I2C speed communication. That is why we don't put them in the DS. But I agree that it is good to have them in the DS. 

Best regards,

Oleh Sapiha