NI SCXI-1162 as a ground switch

[robbjp]

Can the NI SCXI-1162 be used to swich in one of the DIO in ports as a 'GND' to a 3.3V voltage level?  I don't think so but thought I would ask.

In my application the input line to this port is otherwise floating with a low current 3.3V supply to a 1Kohm in series to a CMOS input to an FPGA port.  I see the 360 OHM resistor to chassis ground, so the thought is when a port is made active it actively routes the signal to weak GND through the resistor/diode combination.  If this 1162 can be used to present a ground to a low voltage logicguess my second question is I'm wondering what the port presents to the application input line when the port isn't active?

[Wallace_F]

Hi robbjp,

From the description of your application, it is difficult to tell whether the SCXI-1162 is suitable for your application.  Can you please confirm that you intend to use the SCXI-1162 as a 3.3V logic source to drive your FPGA?

Regards,

Wallace F.

[robbjp]

Yes, actuall it is the 1163 output (open collector).  I realize there shouldn't be trouble in setting a port to GND, but does VCC still need to be referenced to the application circuit?  I've seen in some discussions/threads that VCC MUST be connected to a +V no matter what the application is.

[Wallace_F]

Hello robbjp,

You are correct, according to the SCXI-1163 User Manual, for any output port to work, that port must be connected to a VCC and a ground.

Regards,

Wallace F.

[robbjp00]

Does NI recommend then if the 1163 is to be used to enable and disable an application circuit that only the VCC is supplied to the 1163 as well as the 'port output' connection?  (ie leave ground tied to 1163 ground).

[S_Hong]

Hi robbjp00,

According to page 2-11 of the SCXI-1163 User Manual, we recommend connecting a power supply VCC anywhere between 4.5 - 5.5V referenced from the ground of the particular output port. Note that since the 1163 is an optically isolated digital output device, the ground of this port will isolated from the ground of the other channels as well as the ground of the 1163. So in short, the ground terminal needs to be connected to the reference used to supply the VCC.

I hope this answers your question.