Last night I finally got the computer to talk to the controller/motor!
This has been a little struggle for me, a surprising one. I expected to just hook up the correct step and direction pins from the breakout board to the controller. TTL is TTL right? After carefully checking the connections, I turned everything on, fired up TurboCNC and ..... nothing. Very disappointing!
I've tried swapping cables, changing my port settings, remapping the parallel port pins, even changing power supplies to the breakout board. Nothing worked, so I came to the conclusion that I wasn't getting enough current out of the breakout board. I'm using a CNC4PC board, by the way.
The board I am using claims 8ma per pin.
http://www.cnc4pc.com/Parallel_Port_Interface_Card.htm
Looking for a link, I just discovered that they offer two breakout boards. The "Bidirectional" board has a specification of 35ma per pin!
http://www.cnc4pc.com/Bidirectional_Breakout_Board.htm
The Emerson manual says the controller needs 25ma per pin. I reasoned this is because the TTL lines go directly into a opto-isolator, which need the higher current. So I thought I needed more current from my breakout board.
It turns out to be much simpler! There are two DB25 ports on my computer, one male, one female. My parallel cable, of course, only plugs into one of the ports. I never checked if it was the right one! On opening the PC case, I discovered it was actually hooked up to a serial port. Man, did I feel dumb.
After shelling out $8 (yikes!) to Radio Shack for a gender changer, I plugged everything in and it actually worked! It's silly how gratifying it was, just watching the motor respond as I used the jog controls in TurboCNC.
It wasn't perfect though. I am running TurboCNC in a DOS window within Win98, and I think windows is messing with the timing, making it pause between pulses and limiting the maximum speed. Funny thing is that when I try to run TurboCNC in DOS only mode, it just sends the computer into a reboot.