The current plan is to use a 3Com 3c509B ISA Ethernet card with the hardware that I plan to build and finally give the Color Computer Ethernet capabilities. One advantage of the 509B card is that is has off-loading capabilities in hardware for checksums. The 6809 in the CoCo can use all the help it can get! The other thing about this card is you can purchase them cheap from eBay. At least a year ago you still could... One site that I have found has some example drivers click here . For a detailed copy of the 3Com 3c509B hardware (zipped PDF) click here . Finally, this site has an IP Stack for use with microcontrollers.