Hello:
I am trying to use the display with I2C. I have 1500 ohm pull-ups and am sending at only 20,000 bits per sec. From the CPU side it looks like it works in that I can transmit and get an ACK. I have it sending a single character every 1 second. It prints a variety of garbled characters instead of the the letter "A", "B", etc, every second.
I scoped the SCL line and it looks good. It high signal being a little over 4 volts. I think the problem is the SDA line. I have about minus 0.5 volt all the time. If I disconnect the CPU and the pull-up resistors, the SDA will drop to minus 4 volts. This is just a power supply and display module. Is it supposed to be like that? I was/am being very careful to be sure that my gnd and +5 are on the right pins.
Do you have an idea what might be happening?
Harold
Just to add additional info I have discovered:
There are hardware soldered jumpers on the board that forces it operate in RS-232 or, with some desoldering, you can make it work for I2C. Wasted about 12 hours on this so far. ...and still wasting. The "datasheet" that comes from Digikey just happended to leave that critical info out. The datasheet from Matrix's website just happened to have that little added piece of info.
Now I can scope the two I2C lines and see that the hardware is working. Unfortunately it doesn't work cause it's acting like it doesn't have the proper address. (just ignores the comm) One manual said it was 0x50 and another said 0x5C. I can't get an ACK and it acts like both addresses are wrong. From the manual I am taking the 0x50/0x5C to include the 0 in the first bit for writing...
Do I have an address problem? Or is it deeper. Any help would be appreciated.
Harold
