Not sure what is wrong , but you could check this things:

/root# uname -a
QNX EA869dfc 6.4.0 2008/10/21-11:10:39EDT x86pc x86

/root# usb
USB 0 (EHCI) v1.10, v1.01 DDK, v1.01 HCD

USB 1 (UHCI) v1.10, v1.01 DDK, v1.01 HCD

USB 2 (UHCI) v1.10, v1.01 DDK, v1.01 HCD

USB 3 (UHCI) v1.10, v1.01 DDK, v1.01 HCD

Device Address             : 1
Vendor                     : 0x067b (Prolific Technology Inc.)
Product                    : 0x2303 (USB-Serial Controller)
Class                      : 0x00 (Independent per interface)

USB 4 (UHCI) v1.10, v1.01 DDK, v1.01 HCD


/root# pidin -pdevc-serusb arg
     pid Arguments
149442622 devc-serusb -d vid=0x067b,did=0x2303,busno=0x03,devno=0x01

/root# pidin -pdevc-ser8250 arg
     pid Arguments
   94222 devc-ser8250 -u1 3f8,4 -u2 2f8,3


/root#use devc-serusb
...
...

/root# ls /dev/ser*
/dev/ser1        /dev/ser2        /dev/serusb1

/root# stty -a </dev/ser1
Name:  /dev/ser1
Type:  serial
Opens: 1
+hupcl +cread -clocal -isig -icanon -iexten -echo -echoe -echok -echoke -echonl -echoctl -noflsh -ignbrk -brkint -ignpar
 -parmrk -istrip
-inlcr -igncr -icrnl +imaxbel -opost +onlcr
-isflow -osflow +ihflow +ohflow
 intr=^C  quit=^\ erase=^?  kill=^U   eof=^D   eol=^-  eol2=^- swtch=^-
start=^Q  stop=^S  susp=^Z dsusp=^- reprint=^- discard=^- werase=^- lnext=^V
  min=01  time=00   fwd=^- login=^-   pr1=^[   pr2=5B   pr3=^-   pr4=^-
  sf1=^-   sf2=^-   sf3=^-   sf4=^-  left=44 right=43    up=41  down=42
  ins=40   del=50   rub=^-   can=^-  home=48   end=59
par=none bits=8 stopb=1 baud=57600 rows=0,0

/root# stty -a </dev/serusb1
Name:  /dev/serusb1
Type:  serial
Opens: 1
+hupcl +cread -clocal -isig -icanon -iexten -echo -echoe -echok -echoke -echonl -echoctl -noflsh -ignbrk -brkint -ignpar
 -parmrk -istrip
-inlcr -igncr -icrnl +imaxbel -opost +onlcr
-isflow -osflow +ihflow +ohflow
 intr=^C  quit=^\ erase=^?  kill=^U   eof=^D   eol=^-  eol2=^- swtch=^-
start=^Q  stop=^S  susp=^Z dsusp=^- reprint=^- discard=^- werase=^- lnext=^V
  min=01  time=00   fwd=^- login=^-   pr1=^[   pr2=5B   pr3=^-   pr4=^-
  sf1=^-   sf2=^-   sf3=^-   sf4=^-  left=44 right=43    up=41  down=42
  ins=40   del=50   rub=^-   can=^-  home=48   end=59
par=none bits=8 stopb=1 baud=57600 rows=0,0

reading/writing data from/to /dev/ser1-/dev/usbser1 works for me.

Hope this helps.
Jeevan


> Hi,
> 
> I'm trying to use a USB-UART chipset for which I have invoked the devc-serusb 
> driver. I'm able to get two nodes /dev/serusb1 & /dev/serusb2. The chipset 
> vendor is FTDI. 
> 
> I have connected /dev/serusb1 & /dev/ser1 through this chipset and cable. I 
> write a sample data into /dev/serusb1 and read it from /dev/ser1 but I don't 
> get any data. When I checked with cat /dev/serusb1, I could find the data in 
> it still. 
> 
> My question is what could be the reason behind the written data not getting 
> transmitted out of /dev/serusb1, although the APIs return success? 
> 
> I have treated the virtual serial port the same way as the conventional serial
>  port. Is there anything specific that needs to be taken care for virtual 
> serial ports?
> 
> Thanks,
> Lakshminarayanan.R
> 
> PS: 
> 1) I tried the same chipset in windows with the driver provided by the vendor 
> it works!
> 2) And in QNX host, when I connect /dev/ser1 to /dev/ser2 through cables, if 
> some data is written in /dev/ser1 it is available in /dev/ser2. If I do a cat 
> in /dev/ser1 - no data is there and cat /dev/ser2 gives the output data!