PC Parallel Port BOB (Break Out Boards)

for Stepper Motor Control Signals

Each Stepper Driver really requires only two signals, Direction and Step. The other signals are for configuration of the operating mode can be supplied by manual jumpers. Each PC parallel port has 8 data outputs (D0 to D7) plus some control signals.

The standard way of connecting stepper controllers to parallel ports is like this:

Port
Pin   Axis Signal
----- ---- ---------
02 D0  1   Step
03 D1  1   Direction
04 D2  2   Step
05 D3  2   Direction
06 D4  3   Step
07 D5  3   Direction
08 D6  4   Step
09 D7  4   Direction

The control signals are still available for Spindle motor relay control, etc...This allows for 4 axis control, and is the option supplied with our 4 Axis / +5 Power / Pulse/test / Relay BOB board which really makes the entire thing very easy. And that is the point of a Break Out Board or BOB: To make it really easy to connect everything. A parallel port connector on one end, screw terminals or pin headers on the other, and traces that connect the two. Some boards also include other functions, like optical isolation (more trouble than it's worth). If you don't have the money, buy or scrounge a good quality parallel port printer cable, cut off the printer end, ohm out the wires, and connect as above to your stepper drivers. Done.

Some of those extra control signals are outputs, but they are "open collector" and can not typically change state from low to high very quickly. Because direction usually changes much less often and doesn't need to change as fast, It's possible to use pins 1, 14,16,17 as extra direction lines combined with some of the data pins as step (step needs to change state faster, usually) but I'd be worried about reliability at speed. For example:

Port
Pin   Axis Signal
----- ---- ---------
02 D0  1   Step
14  *  1   Direction ( * nAutoFeed )
03 D1  2   Step
16  *  2   Direction ( * nInit )
04 D2  3   Step
17  *  3   Direction ( * nSelectIn )
05 D3  4   Step
01  *  4   Direction ( * nStrobe )
06 D4  5   Step
07 D5  5   Direction
08 D6  6   Step
09 D7  6   Direction

But then you have no signal for spindle relay, etc... Actually, most of the software available for PC's will specify which Port Pin is to be used for what, or will allow you to specify in the software how you have connected the signals. You just have to find a break out board that matches the wiring you want, or "roll your own" with a custom made board or cable.

If you need more there are two options:

1. Install a second parallel port (for 8 axis) This is actually very doable on most desktop computers. The expansion cards are still very much available. I've seen systems with 3 parallel ports.

2. combine direction signals.

IF your software supports it (never seen one that does), you could technically wire all the direction inputs to one parallel port pin so that the remaining pins are available to step other axis. The software needs to set the direction for the first axis, then pulse the ONE step signal for that axis and continue repeating this process for each axis. Obviously this takes longer, but for some applications, maybe that doesn't matter. Another (serious) issue is that you probably can't drive 7 direction inputs from one parallel port data pin, but a simple buffer amplifier circuit could resolve that issue.

Port
Pin   Axis Signal
----- ---- ---------
02 D0  1    Direction
03 D1  1    Step
04 D2  2    Step
05 D3  3    Step
06 D4  4    Step
07 D5  5    Step
08 D6  6    Step
09 D7  7    Step

So this would allow 7 Axis control from one parallel port. But again, only at lower speeds, watch out for the load on the direction pin.

Again, see our page on the parallel port pins for the actual pin numbers and pictures of the connectors.

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