SC18IM704 - I2C not running after command received

[jjvicente]

Hi,

I am trying to access two I2C devices through a SC18IM704. How ever, when I send a write/read command via UART, no signals appear in the I2C whatsoever.

You can find a transaction screenshot (Read register 0x00 in device 0x4D) (yellow-red are UART, green-blue are I2C):

As you can see, I2C is correctly pulled up, but no commands appear in either direction.

For more info, the SC18IM704 does correctly answer to internal register reads/writes.

Is there any known issue that makes the chip behave this way? 

Regards,

Juanjo

[jjvicente · Accepted solution]

Hi David,

I 've found the root cause of the issue. The SCL pin wasn't correctly soldered (the same pin on three different boards! what are the odds?).

Resoldering again the ICs solved the problem.

Thanks for the support!

Juanjo

[jjvicente]

Hi,

Here I attach an extract of the involved schematic:

I´m converting a RS-485 bus into serial TTL, then it feeds the SC18.

I'm facing other issues regarding the answer timing of the SC18, but I think this issue should be asked in other topic.

[diazmarin09]

Hello Juanjo,

Thank you for your contribution.

In this case, could you please make sure the SC18IM704 device is working properly? I mean, have you tried to read or write the internal registers?

0x52 0x00 0x01 0x50 // Read register 0x00 and 0x02

Besides, could you please measure the SDA and SCL pins directly from the SC18IM704 device? I mean, before the transceiver.

Finally, I would like to recommend the document below. At chapter 4.4, you may find useful sample control sequences that might be useful for you as a reference.

UM11664

Regards,

David

[jjvicente]

Hi,

I have confirmed the SC18 is working properly, here you can see a "getID" transaction: 

Also, I have checked all the slave I2C-devices are ok, by directly driving the I2C bus using a FRDM-KL43Z. They are up and working:

However, still no data on the I2C via the SC18:

Also I have tried to solder a new SC18, same results.

Regards,

Juanjo 

 

[diazmarin09]

Hello Juanjo,

Based on the device ID, it is working properly.

I do assume that the I2C address of your slave device is 0x9A.

As a final test, could you please replace the pull-up resistors? I mean, at SDA and SCL pin. I do recommend using 3.32K value.

Regards,

David

[diazmarin09]

Hello Juanjo,

I hope all is great with you. Thank you for using the NXP communities.

Before going forward, could you please share your schematic? Are you using our evaluation board?

I hope this information helps.

Regards,

David