no data arrives to /usr/lib/cups/myBackend (0 bytes)

[ekkard gerlach]

I print
  lp -d usb-printer -h secondPC -o raw /tmp/myASCII.prn
to the secondPC. "usb-printer" has its own backend to print to 
/dev/usb/lp0:

/usr/lib/cups/backend/myUSB_lp0-Backend:
=========================================
cat - >/tmp/usb-druck2222      <== this file is up to
                                 date and alway 0 bytes!!! Why?
chmod 666 /tmp/usb-druck2222
cat /tmp/usb-druck2222 >/dev/usb/lp0

printers.conf
=============
<Printer usb-drucker>
Info RAW-Drucker auf USB, nicht benutzen
Location
DeviceURI myUSB_lp0-Backend:/tmp/egal3333
State Idle
Accepting Yes
JobSheets none none
QuotaPeriod 0
PageLimit 0
KLimit 0
</Printer>

The directory  /etc/cups/ppd/  is empty. No ppd-Files.

err_log (debug mode) shows no errors! 0 Bytes are printet to 
/dev/usb/lp0 with no errors, okay ...

BTW:  /etc/cups/mime.types und /etc/cups/mime.convs on secondPC
run with enabled "application/octet-stream"

any help?
thx
Ekkard