> xmodem -cy c5400-boot-mz.123-1a.bin
Do not start the sending program yet...
device does not contain a valid magic number
dir: cannot open device "bootflash:"

WARNING: All existing data in bootflash will be lost!
Invoke this application only for disaster recovery.
Do you wish to continue? y/n  [n]:  y
Ready to receive file c5400-boot-mz.123-1a.bin ...
Erasing flash at 0xb8000000

-- Prior to this:
rommon 1 > xmodem -y c5400-boot-mz.123-1a.bin
Do not start the sending program yet...
         File size           Checksum   File name
   2246932 bytes (0x224914)   0x3672fac2    atlantisnet.V1.7.20

WARNING: All existing data in bootflash will be lost!
Invoke this application only for disaster recovery.
Do you wish to continue? y/n  [n]:  y
Ready to receive file c5400-boot-mz.123-1a.bin ...
Erasing flash at 0xb8000000^9\uffff.\uffff\uffff
rommon 2 >

The junk at the end of the Erasing flash line is when I changed port speed on my terminal app when I thought it was stuck after about 10 minutes after the file had finished transfering.