Quote Originally Posted by m_c View Post
Computers are very good at dealing with numbers, but having two matched hardware outputs is better.
By using the software to mirror signals, you can end up with slight timing discrepencies, however most of the time it won't cause any issues.
Could you explain this in very, very great and technical detail? I really don't get it. I'm utterly clueless about CNC machines but me and computers go way back and I'm a bit confused about this concept.

There is no such thing as 'hardware' in this context because the pin assignment of a parallel port is always determined by 'software'. If you attach a printer to the parallel port the computer will use the pins differently compared to how the computer uses them when a scanner or for example a cnc machine uses them. 'Hardware' here is a meaningless concept, devices come, devices go, the signals that are sent down the wire are determined by software just as different ships come and go from a harbor and the ability of a ship to dock with a port is not dependent on the cargo that a ship carries or the people on board a ship, if you can physically fit into the harbour and attach one or more cables to one or more bollards you are officially 'docked' in 'port'. This analogy is why a parallel 'port' is called a 'port'.

Perhaps a different analogy is in order:

Scenario 1 - You are sitting in a room, I walk in to the room with two people that you do not know. I point to the first person and say this is Bob, I point to the second person and say this Fred, they will be working for you. You go away and spend the rest of your life calling Bob 'Bob' and Fred 'Fred'. All is good with the universe.

Scenario 2 - You are sitting in a room, I walk in to the room with two people that you do not know. I point to the first person and say this is Fred, I point to the second person and say this is Bob, they will be working for you. You go nuts and kill everyone in the building, shortly after the universe implodes. This is because everyone knows that it is an irrevocable law of phyiscs that people called Bob must always be introduced before people called Fred.

If you think this is getting a bit ridiculous now you are right...