If your target system does not have an Ethernet port it is possible to transfer files, such as the kernel image over serial port, using ymodem.
On minicom:
RedBoot> load -r -b 0x100000 -m ymodem zImage
Where "zImage" is the file to be transferred.
On minicom press "CTRL + a" and "s", choose ymodem and select the file to be transferred.
