Hi
im new here, so bear with me 
It appears that I accidentaly fudged the adapter. I have a USBtinyISP programmer, and I want to update the firmware on the 8U2.
I also wanted to do it over USB, but i dont know how to put the atmega to DFU mode.
with avrdude, I tried this command
avrdude -p atmega8u2 -c usbtiny -E reset -U flash:w:sparkfun_USBtoSerial_combined.hex
SparkFun-USBtoSerial-master spikey$ avrdude -p atmega8u2 -c usbtiny -E reset -U flash:w:sparkfun_USBtoSerial_combined.hex
avrdude: WARNING: -E option not supported by this programmer type
avrdude: Error: Could not find USBtiny device (0x1781/0xc9f)
avrdude done. Thank you.
Macintosh:SparkFun-USBtoSerial-master spikey$ avrdude -p atmega8u2 -c usbtiny -E reset -U flash:w:sparkfun_USBtoSerial_combined.hex
avrdude: WARNING: -E option not supported by this programmer type
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.01s
avrdude: Device signature = 0x1e9389
avrdude: NOTE: FLASH memory has been specified, an erase cycle will be performed
    To disable this feature, specify the -D option.
avrdude: erasing chip
avrdude: reading input file "sparkfun_USBtoSerial_combined.hex"
avrdude: input file sparkfun_USBtoSerial_combined.hex auto detected as Intel Hex
avrdude: writing flash (7448 bytes):
Writing | ################################################## | 100% 9.50s
avrdude: 7448 bytes of flash written
avrdude: verifying flash memory against sparkfun_USBtoSerial_combined.hex:
avrdude: load data flash data from input file sparkfun_USBtoSerial_combined.hex:
avrdude: input file sparkfun_USBtoSerial_combined.hex auto detected as Intel Hex
avrdude: input file sparkfun_USBtoSerial_combined.hex contains 7448 bytes
avrdude: reading on-chip flash data:
Reading | ################################################## | 100% 6.44s
avrdude: verifying ...
avrdude: 7448 bytes of flash verified
avrdude: safemode: Fuses OK
avrdude done. Thank you.
but serial port device still ist seen in the arduino IDE.
please help me flash the adapter