That's not a true differential output. It's an optoisolator's two
output terminals. Since they're isolated, neither terminal is tied to a
gnd or + so you can connect it high or low.
When tripped, it conducts current (supplied externally) from + to -. It
cannot generate its own voltage, only conduct.
So all you need to do is hook it to a pin with an external pullup.
AFAIK all the 7i47 have a pullup to +5v. Alarm+ to pin, Alarm- to
gnd. The pin will go low when the Alarm signal is active.
Similarly the inputs aren't true differential, they're an optoisolator's
input diode with a series resistor to produce the rated trigger current
when +5v is applied + to -. Due to some esoteric details in how the bus
switch drive output works, these work best if you tie the + to +5v and
use the pin to drive the - to gnd. The signal is weaker if you do it
the other way.
Danny
On 6/17/2017 9:30 AM, Andrew wrote:
Hello,
The stepper drive has open collector alarm output.
Can I use a differential RX input on 7i47s to read it?
Thanks
Andrew
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