Level of TX signal after RESET

I would like to ask a question about the output signal “TX” from the MSC-MOD20.
What kind of output level is the TX signal after reset until the banner is output? (High-Z or weak-pull up/down?)
When measuring the TX pin with an oscilloscope, the level is low during this period.
This level also goes low when you touch the TX pin with my finger.
I would like to set this period to High level, and please answer if is there any good way.

By the way, the conditions are as follows.

  • Directly connected to TX of MSC-MOD20 and input pin of FPGA (Xilix Kintex 7).
  • The input pin of FPGA gives the attribute of weak pull-up.
  • The waveform is measured with a Tektronics oscilloscope.
  • The following waveforms are observed.


When FT234XD from FTDI and MSC-MOD20 are directly connected, the following waveforms are observed.



This story is not about “ALFAT”, but about STM32. Ask on the STM32 forum.
This forum is suitable for talking about ALFAT “software”, but I think you should use stmicro’s forum as a STM32 questions that depend on the hardware specifications.
ALFAT is a monster of a SM32F205RBT6.


What is this? And what GHI product are you using?


ALFAT chip used…

User manual says the manufacturer of the board provides no support, and the user should contact GHI for support.

Those should not be used on any new designs

The TX pin is floating when the CPU is reset. So it depends on the specification of the RX. How much is the sink current?

In general, the following procedure will force TX pin to Vcc level regardless of reset state.

The resistance value should be changed according to the GPIO specification of the device you are connecting.

The waveform below is when ALFAT is connected to MAX10.

Before asking a question here, first do some experimenting with connecting a resistor.
Anything not mentioned in the ALFAT or STM32 data sheet cannot be solved by asking here.
You need to experiment and solve it yourself.

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