UNO Wifi Rev2 cannot connect on start-up

The Rev2 gets connected to my laptop through USB serial. In the IDE the port is visible.
Opening this port in a PureData patch succeeds, but no communication.
With a simple sketch, Serial.println("test") every 2 seconds, nothing comes through.
Reset on the Rev2 is no help.

HOWEVER: when i first start the serial monitor in the IDE, the text comes through, and after that the connection from the PureData patch also gives results.

This problem also happens after an upload with a sketch.

What could possibly cause this curious behaviour?
And what could solve it?

rolf

sorry, forgot to mention i’m on Windows 10

rolf

with another new UNO Wifi Rev2 i get the same problem.

rolf

maybe somebody can tell me what does the IDE send to the arduino when opening the serial monitor,
and if i can emulate that.
it must be some code i guess.

rolf

found with the help of the Puredata forum:

sending a DTR 1 to the port got it working.

with the ‘regular’ UNO DTR 0 or 1 doesn’t influence the communication.

rolf