SC18IM700 fails for unknown reason

[clementg]

Hi,

I am having trouble with the SC18IM700 on a project.

It seems to be failing for no apparent reason. It resets "itself" at random times.

I checked the signals when these resets happen, the RESET and WAKEUP pin remain high. The power line is stable as well. Even with those conditions, I can sometime see the "OK" @ 9600 bauds and the GPIOs going "up" as if they were inputs (GPIOs are pulled-up in my design).

Is there other reset conditions besides : 

• - pulling down the reset pin
• - sending a "Z" commande and pulling down the wakeup pin
• - powering the device down and up again

In my case, the resets occur without any of these conditions...

Thanks for your help

[clementg]

Hi,

I think I might have figured out what caused my issues : the UART frequency of my MCU drifts randomly by up to 8%, which is quite important  @ 115200 bauds.

Can this explain why the SC18 would resets itself ? Can a corrupted frame make this behaviour occur ?

Thanks.

[scott_register]

clementg david_diaz are you able to explain how to set the Baud Rate registers to obtain the desired baud rate?   I can't for the life of me figure out how that equation works to set the baud.  the [16 + (BRG1 , BRG2)] portion is very confusing...I'm not sure how to handle the ordered pair in that equation and how it correlates to setting the Baud Rate.  The default values, supposedly for 9600 baud, are BRG1 = 240 and BRG0 = 02.  I can't at all find the math to perform to turn those two values into 9600 and therefore am unable to establish a new baud rate.

[david_diaz]

Hello Clement,

I hope all is great with you.

First, please make sure you have the correct configuration.

Please review the file attached to this response. You may find the OM6272 schematic (evaluation board for the SC18IM700 device). I recommend using it as a reference for your design.

Have you configured your device correctly? Please share your results.

I hope the information provided was useful for you.

Regards,

David

[clementg]

Hello David,

Thanks for your answer.

My design seems to be correct, every GPIOs are pulled up with 100k resistors, the Reset and Wakeup pins are also pulled up with 1k resistors, the reset pin is controled by my MCU and the wakeup is left "floating" with its pullup resistor (not connected to anything else) . I have a 0.1uF filter capacitor on VCC (3.6v) and i²c bus is pulled up with 4.7k resistors.

When unexpected resets occur, both reset and wakeup signals are steady...

I managed to monitor the failures on multiple devices and I see that this happens on just a few of my PCBs.

There is no visible hardware difference and software configurations are identical.

The only difference is in the actual data sent onto the UART.

Is there a way to lock the bridge in a weird state implying a reset by sending unusual commmands onto the UART or from the i²c ? Or any other reason that would cause a reset ?

Thanks

[clementg]

Hello again,

I managed to correlate unexpected resets of the SC18 with "breaks" on the UART.

Can you please tell me if a break condition is supposed to reset the bridge or if it's an unrelated behaviour ?

Thank you

[darioarias]

Hi Clement,

Another factor that could be causing the reset is the timeout condition. The time-out register is used to determine the maximum time that SCL is allowed to be LOW before the reset occurs and this can be correlated with the break on the UART.  You can try to stretch the time in this register or completely disable it.

Darío