Hello Greg, I am using pl2303.c ( USB to serial device driver ) to communicate to various devices connected in parallel using RS-485 interface card. I am now able to separate the Address byte and data bytes.Driver send the Address byte properly but when it tries to send the data bytes following error occurs, pl2303_mcm ttyUSB0: pl2303_write - failed submitting write urb, error -22. I have also attached the kernel log. /home/teleset/Desktop/USB-Serial/pl2303_mcm.c: pl2303_write before any thing - port 0, 9 bytes /home/teleset/Desktop/USB-Serial/pl2303_mcm.c: set_control_lines - value = 3, retval = 0 Data in The BUF 0 is -----> 02 Data in The BUF 1 is -----> 08 Data in The BUF 2 is -----> 00 Data in The BUF 3 is -----> 00 Data in The BUF 4 is -----> 00 Data in The BUF 5 is -----> 00 Data in The BUF 6 is -----> 00 Data in The BUF 7 is -----> 00 Data in The BUF 8 is -----> f8 pl2303_mcm ttyUSB0: pl2303_write - length = 1, data = 02 /home/teleset/Desktop/USB-Serial/pl2303_mcm.c: After the first urb submission count = 9 and length = 8 pl2303_mcm ttyUSB0: pl2303_write - length = 8, data = 08 00 00 00 00 00 00 f8 pl2303_mcm ttyUSB0: pl2303_write - failed submitting write urb, error -22 /home/teleset/Desktop/USB-Serial/pl2303_mcm.c: pl2303_write_bulk_callback - port 0 /home/teleset/Desktop/USB-Serial/pl2303_mcm.c: set_control_lines - value = 0, retval = 0 Kindly help me. Raj. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html