title: TrendNet TU-S9 RS232/USB and OS X
body: <p>I recently bought a TrendNet TU-S9 USB to RS232 converter.  I need to talk to microcontrollers that use RS232 at 9600 baud.  The code I have for a Linux box works fine.  I installed the drivers according to the instructions on my laptop and a Mac Mini both running OS X 10.6.7.  I changed the device to /dev/cu.usbserial.</p>
  
  <p>Here's what happens. It sure does look like communication will work the first time I try it.  But if I exit the process I can't write to the serial device anymore.  If I unplug the USB connection and plug it in again, then I can go one more time.  I.e. it looks like plugging in the USB connector is what is necessary to get things reset to a usable state.</p>
  
  <p>When I get the error the second time I try to start the process, I can open the device, but the error happens the first time I try to send a byte over the serial interface.  The error from perror is "Serial: No such file or directory".</p>
  
  <p>I can get around this problem by writing a second program that merely opens the cu.usbserial device and then loops forever.  This doesn't seem like the best way to fix it, though.</p>
  
  <p>Has any one seen this behavior?  Can anyone replicate it?  Does anyone know how to fix it?</p>
  
  <p>Note: this might be related to a previous post <a href="https://stackoverflow.com/q/3976">Programmatically talking to a Serial Port in OS X or Linux</a>, or it might not.</p>
  
  <p>Eric</p>