Experiments with resistance in the 5V power supply line to the TXS0102 have proven fruitless.
Values above about 3K allow everything on the 5V side of the I2C to run fine, but there is no communication on the 3.3V side.
Values below 1.2K start to allow communication on the 3.3V side, but it is unreliable.
Values below 680Ohms allow perhaps a little better communication on the 3.3V side, but kill all communication on the 5V side.
I've switched the OE (Output Enable) pin of the TXS0102 to be powered by 5V, instead of 3.3. To no avail.
We have another hacked up prototype that uses an ADAFRUIT 757 level shifter (https://www.digikey.com/product-detail/en/adafruit-industries-llc/757/1528-1007-ND/4990756) instead of the TXS0102.
This prototype behaves the same way. One thing that we can do with the ADAFRUIT part is actually desolder and replace pullup resistors internal to the level shifter.
We're also looking at the datasheet for the Focaltech FT5406 controller, which is what the touchscreen uses.
There are only two knowns right now:
-The motherboard has pullup resistors onboard, because we can operate the 5V I2C without any pullup resistance or level shifters (which have internal pullup resistance). So any pullup resistance that we apply
-The motherboards that work (all I2C, both 3.3V and 5V communicates) are among the first batch that we bought, with a revision 5.05. Later motherboards (revision 5.07) don't work. We have hacked BIOS and software to match, to no avail. So there is some hardware difference on the motherboard that is sensitive to our I2C design.
Values above about 3K allow everything on the 5V side of the I2C to run fine, but there is no communication on the 3.3V side.
Values below 1.2K start to allow communication on the 3.3V side, but it is unreliable.
Values below 680Ohms allow perhaps a little better communication on the 3.3V side, but kill all communication on the 5V side.
I've switched the OE (Output Enable) pin of the TXS0102 to be powered by 5V, instead of 3.3. To no avail.
We have another hacked up prototype that uses an ADAFRUIT 757 level shifter (https://www.digikey.com/product-detail/en/adafruit-industries-llc/757/1528-1007-ND/4990756) instead of the TXS0102.
This prototype behaves the same way. One thing that we can do with the ADAFRUIT part is actually desolder and replace pullup resistors internal to the level shifter.
We're also looking at the datasheet for the Focaltech FT5406 controller, which is what the touchscreen uses.
There are only two knowns right now:
-The motherboard has pullup resistors onboard, because we can operate the 5V I2C without any pullup resistance or level shifters (which have internal pullup resistance). So any pullup resistance that we apply
-The motherboards that work (all I2C, both 3.3V and 5V communicates) are among the first batch that we bought, with a revision 5.05. Later motherboards (revision 5.07) don't work. We have hacked BIOS and software to match, to no avail. So there is some hardware difference on the motherboard that is sensitive to our I2C design.