arduino - Serial port shown in device manager but unable to access/found? -

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i've installed arduino virtual usb serial port driver, it's appeared com4 on device manager. double checked listing available serial ports in powershell

> [system.io.ports.serialport]::getportnames() com1 com4

however, when try echo serial port, says not exist

> echo helloworld > com4 system cannot find file specified.

i trying upload firmware in arduino, kept getting denied port. trying different usb gives me same result. wrote small program test serial port , error:

the serial port "com4" not exist.

the device name of serial port on windows \\.\comn n port number. device driver can emulate dos device name, "com4" if chooses so, simple in device driver code. that's increasingly rare thing do, port numbers larger 2 , port numbers larger 4. seeing echo command fail not unusual.

a serial port cannot shared, can opened once process , else tries open fail-whale error_access_denied error code. so, serial ports sit @ bottom layer of osi model, there no protocol arbitrates access port. or put way, operating system has no guidance on should data port receives. there can 1 candidate, process opened port first. error message got not unusual, have make sure nobody else using port. including arduino serial port monitor.


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