Issue with the WIZ105SR on RXD from Serial port

[jmora]

We are facing a strange behavior on a WIZ105SR module when transmitting data on the serial port.

We succeed when connecting the WIZ105SR to the PC and transmitting data using a virtual COM on the PC. However, when the MCU in our target board responds, we observe that the voltage at pin 3 of J1 (RXD) is always high (3.3V):

Seems like the RXD pin on the GC89L591A0-LQ44I of the WIZ105SR is set as an output and keeps always high level.

Could you please support us on this and check what we are doing wrong on the device?

Thanks in advance.

Regards, Julio

[Scott]

Hi jmora

I suspect transistor circuits.

A typical level shift circuit is shown below.

Remove WIZ105SR and check the waveform of CHANNEL 3.

Thank you.