you can toggle the output of the DIO-24 from TTL high to TTL low using software, so that essentially is a pulse. You need to make sure that the current sinking and sourcing spec for the DIO-24 fits your stepper motor. This digital device is probably not the best solution to control a stepper motor. You might want to take a look at the motion control products offered by National Instruments: for open loop look at the PCI-7314, if closed loop with encoder feedback, look at the PCI-7324 or maybe the counter/timer devices: NI-660x devices that will be able to generate single pulse, pulse train, etc.
