Matrix Orbital Corp

I'm having trouble getting I2C to work on an LK162-12 display. I have three questions.

1) I'm driving the display in a 3.3V system (my I2C bus has pull-ups to 3.3V, not 5V). What is the threshold (Vih) for the I2C input on the LK162-12? Normally, this works because 3.3V is usually higher than the Vih of most devices, but maybe it matters for the LK162-12.

2) My I2C interface operates through software bit banging and SCL is running at 10 KHz, not 100 KHz. Is there any reason why this should be a problem? Is there a lower limit to the SCL clock speed?

3) One version of the manual (the web version of the manual from 2 months ago) for this module said "The LK162-12 does not work on I2C by default; one modification has to be done, as shown in the picture." But, there is no picture and there is no description of the modification. This text used to be the first paragraph of section 2.1.4, I2C Communications. The new PDF version of the LK162-12 User's Guide does not have this statement. Was this a typo? Can I ignore this statement?

Thanks

Mike

1) All of our displays require a 5V I2C signal, 3.3V will not work.

2) No it will not be a problem.

3) I don't remember that, sorry... You do not need to do any modifications to the LK162-12 to work with I2C. The most you will have to do is set the I2C address if you don't want to use the default one.

Thanks for your quck response. Just a clarification about the 3.3V/5V thing...

I'm powering the LCD module off 5V, of course, but the signals (SCL and SDA) are pulled high to 3.3V, not 5V. In the past, this has worked fine with most 5V I2C devices because the Vih of a typical IC is 2.4 V, and the 3.3V pull-up exceeds 2.4V, hence meeting the required logic 1 voltage. But, since I am unable to get the panel to work in my system, I'm wondering if the Vih for SCL and SDA are higher on the module than is common.

If you could provide the Vih for SCL and SDA, that would be great. Either that, or I suppose I can look that up by checking the datasheet for the PIC microcontroller you are using on the board. I was just hoping you could tell me straight away. Alternatively, can you tell me for sure that a 3.3V SDA/SCL has failed to work in the past.

In the mean time, I plan to test the modules on an I2C Hardware Analyser (that is 5V or 3.3V capable), but I haven't had a chance to do that yet.

Oh, and the module worked fine through the RS-232 connector.

Thanks.

Mike

The I2C is 5V levels, it will not work on 3.3V... sorry... Glad to hear it works other then that.