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Forum : Digole Serial Display :

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I2C reads not working with 3.3v processor

 I have been trying to get a v2.x touch screen to work with a Particle Photon (STM32F205 based) using I2C.  Writing to the device works well but when I try to read from it (eg. touch), the display will freeze and no data can be read on the processor.  Here is what I tried:

1. Power the device via Vusb (minus diode drop) which is about 4.7v

2. Pull SDA/SCL via 10K resistors to that voltage since the I2C pins of the Photon are 5v tolerant

3. On a logic analyzer I can see a two bytes being returned from the display but with NAKs for both

3. The I2C then hangs along with the display (which must be reset to work again).

4. Tried powering with 3.3v (same with pull-ups) and same thing

I tried shorting the display resistor as suggested in another topic (pertaining to ESP8266).   However, doing so caused the I2C to hang on first read request with no bytes returned.

I have not tried the display in serial or SPI modes yet.  I have also tried a v3.0 display with same results.

RE:I2C reads not working with 3.3v processor

There are 4 bytes should be returned from the display if you send "read touch screen" command, you should read all of these 4 bytes to your controller, otherwise the display only can receive the on comming data into the receive buffer, but will not excute them until all 4 bytes of data read.

Similar with other read data functions, your controller must read all expected length of data out of the display, then let the display run following commands.

RE:I2C reads not working with 3.3v processor

 I should have been more specific.  I am trying to run the Digole_Touch_Screen_Bat_Aux.ino example and the code won't read any of the values as previously detailed.

RE:I2C reads not working with 3.3v processor

 I should have been more specific.  I am trying to run the Digole_Touch_Screen_Bat_Aux.ino example and the code won't read any of the values as previously detailed.

RE:I2C reads not working with 3.3v processor

 Can you take a picture on the component's side of the module?

If the module is older version of PCB, you need short the R2 resistor or use a week pull up (like 20K) on SCL line if you don't use Arduino.

RE:I2C reads not working with 3.3v processor

The board shows V2 on the backside.  I did short R2 and have 10K pull-ups and that did not work.  Now I am working with SPI and noticed that only software SPI will work even if I use a 230Khz SPI clock.  The data seems corrupted on the reads but ok on the writes.

RE:I2C reads not working with 3.3v processor

Please take a picture, and let we see if any of the components missed on the board, you seems ordered them in June 2015, you may need to refer to the old Arduino lib (for products early before Dec 2015).

RE:I2C reads not working with 3.3v processor

 I'll post a picture tonight.  For my own information, where would I find the "older" library?  What would be nice is a nice matrix of firmware versions and when they were released along with what the changes are.  Perhaps another matrix of hardware versions, what they look like and which library to use (along with a link to download).

I have purchased units in the past that were NOT the latest firmware release at the time and no way to update them.  Again, it would be good to know that when I purchase a unit, it is the latest version of the hardware and software for that model.  If not, that should be clearly indicated on the product page.

RE:I2C reads not working with 3.3v processor

We always continue to improve our products day by day, so, at the time you purchased the product, it was the latest version of hardware and firmware on that day.

You can find the lib here:

http://www.digole.com/forum.php?topicID=486

RE:I2C reads not working with 3.3v processor

 Haven't posted a picture yet since I was busy working on switching to SPI mode.  I still want to post a picture since I really want to get I2C working as well.

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