LK202-25 I2C Hardware problem?

[markb]

Hi. I've just bought two LK202-25 s and can't get either of them to talk via I2C. I have a device that uses a PIC 18F452 and has an RTC and a EEPROM on board using the I2C interface.

I also have a LCD0821 rev 1.4.

I have been using the LCD0821 successfully and have not modified my code.

I have wired the LK202-25s using the same connections as the LCD0821 on the four pin connector. (The LK202-25 manual has an error where it describes the pin out so I need confirmation that this is correct)

I have used the software provided and an RS232 connection to a PC to set the I2C address to 50 (hex).

I have removed the solder blobs from the '232' pads and put them on the 'I2C' pads. There are some more 'I2C' pads near the four pin connector but I have not touched these - I am assuming that they are for an optional connector?

When I plug the LK202-25 into my PIC board the program stops executing because it hangs on the I2C write command (I have no timeout!) If you unplug the display it continues running. This would seem to indicate that the I2C lines are being shorted in some way. If I plug in the LCD0821 it works as before.

I have tried reversing the I2C bus connections and then the PIC continues to run, but nothing is displayed....

Any ideas or suggestions anyone???

Mark.

[markb]

I have checked the LK202-25 boards with a meter and the SDL / SDK lines are connected to the correct pins on the 16F877 PIC .... I'm suspecting the firmware is incorrect??

The LK202-25s are R2.2
One has a sticker 2815-05M11, the other 2814-05M11

One has 0539/6 on the board, the other 0538/5

Mark.

[markb]

OK, I've sort of fixed it but I'm not happy with the solution.

It seems to be the pull up resistors on the I2C lines.

My origional design used 10K resistors on both SDA and SCL. This worked fine with various I2C devices including the LCD0821.

I read the posts here regarding I2C and then tried replacing them with 4K7 as that seems to be the value recomended by Matrix Orbital. Still no joy, so out with the scope. The SCL line was hovering around 3V whereas the SDA line was a healthy 5V. In order to get the display to communicate I have to have 4K7 on SDA and 2K2 on SCL.

Surely there is something wrong here????????

Mark.

[Tom]

Hi Mark,

Thank you for posting at Matrix Orbital.

I have contacted you via email.

Best Regards,

[markb]

Thanks Tom!

I did as you suggested and lifted the pin on the RS232 chip. Both displays work fine now with my original 10K pullups.

Is there any reason why you recomend 4K7?

If we get the order we are expecting we will need more displays - is there any way we can guarantee to get ones we don't need to modify?

cheers,

Mark.

[Tom]

The 4.7K was a common value I used with my I2C tester, so I suggested the 4.7K resistor.

The next revision will guarantee that you won't need much modifications. The next revision will be released early next year. If you would like the units I2C rady, you can possibly set up a custom by contacting sales@matrixorbital.com .

Best Regards,