I2C Logic Levels

cthomas · Post by **cthomas** » Thu Mar 18, 2010 10:11 am

I'm trying to communicate with an LCD0821 display using I2C with my TI MSP430 microcontroller.

I was wondering what voltages levels the LCD0821 considers logical high and logical low, so I know what voltage I should pull the SCL and SDA lines to. This doesn't seem to be specified in the datasheets for the LCD0821, and while I understand I2C is more of an ordering specification for the data, I would still like to know if I'm pulling the lines too high for the LCD to read the data i'm sending.

Raquel · Post by **Raquel** » Fri Mar 19, 2010 9:46 am

Hi,

Thank you for posting on the forum.

The specs on the I2C SCL and SDA lines are :
VIL - 0.5V to 0.3Vcc
VIH - 0.7Vcc to Vcc + 0.5

For the LCD0821, Vcc is 5V. Please make sure that your pull-ups are connected to 5V ( max is 5.25V).

I hope this helps.

Best Regards,

cthomas · Post by **cthomas** » Fri Mar 19, 2010 11:31 am

My target platform is a TI ez430-RF2500 development board, which claims to only be able to pass up to Vcc=3.3v to the input of any given pin on the target board.

Does this mean I need some kind of boost or driver to connect the LCD Display via i2c? I've tried pulling the lines up to 5V, and it does not seem like the clock transitions are actually occuring on the lines.

Raquel · Post by **Raquel** » Fri Mar 19, 2010 3:22 pm

Pulling the I2C lines to 5V so long as your TI controller can handle the voltage will be the best case scenario so that there is no need for level translation.

Otherwise try the TI PCA9306.