Hi! Regarding the USB-serial port, I’ve seen the following notes in the schematics for the Colibri Evaluation Board v3.2A and Aster v1.1B carrier board:
It has been found that the FTDI IC is
backfeeding via Colibri module via
RTS and CTS signals. So it is recommended to use an isolation
circuit (like tri-sate buffers)
between Colibri module and FTDI IC
(IC12).
It has been found that the FTDI IC is
backfeeding via module RxD signal.
So, it is recommended to use an
isolation between the Colibri module
and FTDI IC (IC2).
So, how would the tri-state buffers be connected for the RTS, CTS and RxD signals? Or what other solution is there for avoiding this problem?
Thank you for clarifying this.
Hello CristianM,
Ok here some background on this. The FTDI chip is powered via the debug USB port. That means if the colibri is not powered on yet but the FTDI chip is already powered via an external USB host the RTS and CTS signals inject power into the colibri which could lead to some undefined state when powering up the colibri or other issues.
If you are designing your own carrier board you would prevent this by isolating the FTDI chip with a tristate buffer and control the activation of this buffer e.g. with the power of the colibri module so that the module is active when the buffer is active.
When you are developing with the Evaluation board just make sure the colibri is powered on before you plug in the USB.
Best Regards,
Matthias
Hello ChristianM,
can you tell me which document you are referring too?
Best Regards
matthias
