When the 3.3V is apply to ADM0302, I have (One Time on two) the transmit output that rise up then go down à -6.6V. This cause an unknown charater on my RS232 link.
I want to ask whether you let the input TIN floating or not when you captured the waveform above, could you please probe the waveform including the Tin Tout and VCC pins?
What is the signal named "oe_micro"? I would suggest you add a pull up resistor on the Tx_in signal line to see whether there is strong logic low output when processor is powering up.
So based on the situation, I think we'd better solve this problem from the processor side, do you use the UART module or the software simulated IO pins for UART function? Does other general-purpose IO have this power up issue? If possible, try other signal pins.
Thank you for answerbut I thought to have found the problem.
The processor connected to Tin put some time a low level on Tin.
The next waveform show it.
The processor drive a low level on Tin at power on :
The processor does not drive a low level on Tin at power on :
I try to drive the OE# of the processor to GND, but it's the same, the output of the processor is some time low at power up.
The processor is a MCF5307CFT66B
The oe_micro is the output enable of the processor, so after this waveform, I connect this pin of processor direct to ground, but not change, some time, the processor drive to TX-in at low level during power up.
I have pullup on Tx-in on ADM3202, so it's case, the processor drive a logic low during power up.