Hi Greg,
The simple answer is that yes, 10base2 is LOTS easier from the processor point of view. But 10baseT isn't too bad either.
Why?
Like RF, 10base2, and 10base5 for that matter are a single coax cable. Because of this there is no possiblity of sending data in both directions at once. From the CPU's point of view it is either sending OR receiving, but not both. So the cpu doesn't need to try to do 2 things an once. It can turn off interrupts and devote it's full attention to the incoming or outgoing packet.
This is not the case with 10baseT which has 4 wires and can under certain circumstances be sending in both directions at once. Another problem is that 10baseT ordinarily runs with a "keep alive" signal when the line is otherwise "idle". This would mean that the CPU would have to sending these pulses "all" the time.
You suggest that both 'require' a Media interface chip. While this is "always" done, it is really optional. If your look around you will see examples of 10baseT and 10base2 interfaces being done without special chips and without transformers. Eliminating both actually makes the CPU interface cheaper and easier!
In fact it is most tempting to eliminate both of them and then note that the product must be close to a "hub" of some type. Since hubs are very cheap ($5-10) this is not really a problem! Let someone else buy those parts and sell them to you as a "hub" or whatever.
And to come straight to your "question". Yes, you most certainly CAN bit bang 10base2 or 10baseT packets. You have just got to be careful about program timing. You CAN also receive VIA the same method.
That is what I was asking. I have looked at this many times and done it at lower data rates and it works VERY well since you can easily control ALL the details with the CPU code rather than have chip problems that you can't fix easily.
Recent CPUs have gotten fast enough that it ought to be pretty easy to do the whole ethernet interface in software, as 10base2,10baseT have pretty simple bit patterns.
Driving the output line can be done with a 74hc04 or similar chip. Receiving means pre-biasing a gate as a line receiver. I have found it desirable to have some sort of chip between the CPU and the line. That way electrical surges on the line don't burn out parts of the CPU :)
Hope the above helps :)
Happy hacking,
wiz
