Simple I2C question help

[merkin]

Without getting into specifics, i have a simple question.
If i remove the pullup resistors of I2C bus lines should i still be getting a voltage reading on those same I2C bus lines when the entire circuit is powered.

The I2C bus is pulled up to 3v via 2k2 resistors. but when i remove the resistors i still get ~2.8vdc when the entire board is powered. Is this right? I understand the I2C bus lines are open drain. could they be floating that high or is it more likely that one of the three I2C devices in the circuit are fried and outputing volts on its sdc or scl pin?

Thanks in advance.

 

[pk_volt]

From what I recall, you mentioned they're open drain, which means the pins should either be floating, or grounded. Maybe check if you have the pin configuration right on your micro controlller to ensure it's an I2C pin, and not a digital I/O or something

 

[ckshivaram]

Pull ups are not mandatory in the circuit if you are using just a couple of devices. Pull up's are required when you interface more number of devices. It works fine with upto 7 to 8 devices without pull up. It also depends on the slave you are interfacing.

 

[merkin]

Please just answer the question if you know the answer.
(Should there be DC voltage on the I2C bus lines when the pullup resistors are removed?)

i am 100% sure the pins are sda and scl.

also i am 100% sure that pull-ups are needed.

 

[pk_volt]

Hi there,

Have you read the datasheets for your I2C components to answer your questions?

 

[merkin]

Hi there,

Have you read the datasheets for your I2C components to answer your questions?

have you read my question?

i would not be here if i could find the answer to my question in the datasheets.

if it depends on the i2c devices themselves than just say that so i can continue my diagnosis.

 

[ckshivaram]

Please just answer the question if you know the answer.
(Should there be DC voltage on the I2C bus lines when the pullup resistors are removed?)

i am 100% sure the pins are sda and scl.

also i am 100% sure that pull-ups are needed.

there are many projects where i achieved the results without pullup upto 6 devices. read data sheet for further information, voltage exists even if you remove the pull up resistor, check with multimeter......