help

while connecting usb gps modem is is showing.
 usb 1-1 : new full speed device using s3c2440-ohci and address 2 
 usb 1-1:configuration #1 chosen from choice

how to read data coming from it.

If you want to keep it simple, read the GPS sketches on the Arduino site.
If not, search 'GPS' in the forum here and you should find a link to high
quality GPS libraries.  --  Suggestion: Use a more descriptive topic name
in the future.

open("/dev/ttySAC1", O_RDWR | O_NOCTTY | O_NONBLOCK) is to read com port
in similar passion how we open usb port and read

You wrote gps modem. Do you mean GPS navigation? Or GSM/GPRS MODEM?

ls /dev then plug in the device and ls /dev again to see what it is called.

gps  modem
 it is call as 1-1.
i try to open in this manner.
open("/dev/1-1", O_RDWR | O_NOCTTY)
its not working

Sorry, what is a "gps modem"? Does it have a part number or name?

SIM18 _EVB_v1.02

GPS means Global Position System. GPS modem is a hardware device in my
project we used to interface with Friendly ARM Mini2440.