title: GNU SCREEN - USB serial tty communication problems with MAC OS X 10.8.2
body: <p>we succesfully manage USB to serial communication with a device with Putty on Windows 7 and GNU screen on LINUx but half fail to do so with Terminal / screen on MAC OS.</p>
  
  <p>simple basic communication setup is required on the LINUX windows machine :</p>
  
  <blockquote>
    <p>57600 bps, 8 bits , no parity, no flow control</p>
  </blockquote>
  
  <p>the device mounts succesfully and is profiled as described here ( sorry in French) :</p>
  
  <blockquote>
    <p>Identifiant du produit:    0x6160</p>
    
    <p>Identifiant du fournisseur:    0x03eb  (Atmel Corporation)</p>
    
    <p>Version: 1.10</p>
    
    <p>Vitesse:Jusqu’à 12 Mb/s</p>
    
    <p>Identifiant de l’emplacement:  0x06200000 / 2</p>
    
    <p>Courant disponible (mA):500</p>
    
    <p>Courant requis (mA):0</p>
  </blockquote>
  
  <p>a cu.usbmodem621 and a tty.usbmodem621 do appear in the list of
  ls /dev/tty* or ls /dev/cu*</p>
  
  <p>we activate screen using the following screen command on terminal.app</p>
  
  <blockquote>
    <p>screen /dev/tty.usbmodem621 57600</p>
  </blockquote>
  
  <p>or </p>
  
  <blockquote>
    <p>sudo screen  /dev/tty.usbmodem 57600</p>
  </blockquote>
  
  <p>initally no screenrc file existed, I eventually created one to marginally tune the terminal settings and make sure that there was no flow control :</p>
  
  <blockquote>
    <p>defscrollback 5000</p>
    
    <p>termcapinfo xterm* ti@:te@</p>
    
    <p>defflow off</p>
    
    <p>hardstatus alwayslastline "%{rk}%H %{gk}%c %{yk}%M%d %{wk}%?%-Lw%?%{bw}%n*%f %t%?(%u)%?%{wk}%?%+Lw%?"</p>
  </blockquote>
  
  <p>I have tried without specific drivers, then with the 2 following references</p>
  
  <p>FTDI <a href="http://www.ftdichip.com/FTDrivers.htm" rel="nofollow">http://www.ftdichip.com/FTDrivers.htm</a></p>
  
  <p>Prolific PL2303 <a href="http://osx-pl2303.sourceforge.net/" rel="nofollow">http://osx-pl2303.sourceforge.net/</a></p>
  
  <p>I have also copied and pasted all the settings listed on a 
  stty -a 
  as per the LINUX machine. Here they are :</p>
  
  <blockquote>
    <p>speed 57600 baud; 92 rows; 145 columns;</p>
    
    <p>lflags: icanon isig iexten echo echoe echok echoke -echonl echoctl -echoprt -altwerase -noflsh -tostop -flusho pendin -nokerninfo -extproc</p>
    
    <p>iflags: -istrip icrnl -inlcr -igncr ixon -ixoff ixany imaxbel iutf8 -ignbrk brkint -inpck -ignpar -parmrk</p>
    
    <p>oflags: opost onlcr -oxtabs -onocr -onlret</p>
    
    <p>cflags: cread cs8 -parenb -parodd hupcl -clocal -cstopb -crtscts -dsrflow -dtrflow -mdmbuf</p>
    
    <p>cchars: discard = ^O; dsusp = ^Y; eof = ^D; eol = ;  eol2 = ; erase = ^?; intr = ^C; kill = ^U; lnext = ^V; min = 1; quit = ^\; reprint = ^R; start = ^Q; status = ^T; stop = ^S; susp = ^Z; time = 0; werase = ^W;</p>
  </blockquote>
  
  <p>In ALL cases, the device correctly receives and interprets all commands we send from the screen terminal window but screen fails to display any communication FROM the device.</p>
  
  <p>I have tried Goserial as well a Zterm with the same result.</p>
  
  <p>any hint of what is going on ? </p>