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ADSP-21469 TWI Adress Disappears if another device is added to the bus

Question asked by flying-egg on Jun 19, 2018
Latest reply on Jun 20, 2018 by AlClark

And it's me again with a Problem. I'm sorry to post again, but I unexpectedly encountered another brickwall.ow I 


I have microcontroller communicating with the ADSP-21469 EZ-Kit Lite via I2C. Now I need to add another I2C device to the bus, a display. The display has a 5V I2C line, but also an integrated level shifter with MOSFETs. So I can use 3.3V SCL/SDA Pins on this display module.


But as soon as I connect this device to the bus, the ADSP-21469 does not receive any I2C messages any longer. So I connected an I2C scanner and the result was the following:


- If only the ADSP-21469 EZ Kit is connected to the bus I can see the DSP TWI adress and the adress of the tempsensor

- if I use the SW3.7 and SW3.8 to cut the connection to the sensor, only the DSP adress is showing up

- if I connect the display module with the level shifter, the display adress shows up but the the DSP adress is gone

- if I turn on again SW3.7 and SW.38 the temp sensor shows up again, but the DSP adress is still gone

- if I disconnect the level shifter, the DSP adress again shows up immediatly


What really throws me off, is that the temp sensor can be detected on the I2C bus no matter what. Only the DSP adress disappears if the display is added to the bus. That makes me feel that I missed somekind of TWI configuration that can help me, because the wiring should work properly with the temp sensor showing up.


What may cause this problem?