generated pulse fall time with PIO16XE50 and SCB68 is wrong

[ddel]

I'm using a PCI MIO 16XE50 and an SCB68 with LV 8 to generate pulses signals to a stepper motor controller. I'm using the Labview generate pulse vi and the rise and fall time of the pulses is not correct. Information on the NI web site says that the rise and fall time should be less than 50 ns. My pulses drop from 5 V to 2.5 V, stay at 2.5 V for 250 ns, then fall. Same profile on the rising edge. This seems to happen either with the counters or the digital lines. I think this is causing the stepper controller to see two falling edges because it often makes two moves instead of one.

Is the 250 ns pause normal for this hardware? Is there some calibration or setting that needs to be adjusted?

[Andr3s_Br3n3s]

Hi ddel,

Here is the manual for PCI MIO 16XE50 

http://www.ni.com/pdf/manuals/370717c.pdf

How is your hardware configuration for the motor? how much current the stepper motor controller need? and the motor?

Have a great day

[ddel]

The PCI board just activates an optically isolated digital input on the stepper controller so all the drive parameters to the motor should be irrelevant, but the controller takes 48 VDC at about 50 mA and supplies 2 A at 3 V to the stepper (in the several phases of course).

The maximum current to the digital inputs on the controller is listed at 8 mA.

But even with the SCB 68 not connected to the stepper driver I see the same 250 ns step on either the counter output or the digital outputs. The specs say it is supposed to be 1. 5 ns.