https://ni.lithium.com/t5/Counter-Timer/Signal-modified/m-p/570779#M5259 <DIV></DIV>It sounds like PFI9 (CTR0 GATE) is trying to drive the signal as well. Try disabling the PFI9 output in software.<BR /><BR />If that's not the problem, it's possible (though admittedly unlikely) that your square wave has a very high source impedance, so high that it cannot overcome the ~50 kohm pull-up resistor at the PFI9 input.<BR /><BR />Hope this helps,<BR />Ed<BR /><BR /><DIV></DIV> Sun, 26 Aug 2007 17:12:18 GMT EBL 2007-08-26T17:12:18Z https://ni.lithium.com/t5/Counter-Timer/Signal-modified/m-p/568436#M5253 <DIV>Dear,</DIV> <DIV>&nbsp;</DIV> <DIV>I'm using a 6024E DAQ card. I've connected a square wave (0 V: LOW; 4,5V: HIGH) to the first channel of the analog input (differential mode). However once I connect this signal also to the gate of the counter 0 to measure the frequency as well&nbsp;I&nbsp;notice in my acq. graph that my square wave is&nbsp;modified (4 V: LOW; 4,5 V: HIGH).</DIV> <DIV>&nbsp;</DIV> <DIV>Any help is welcome,</DIV> <DIV>Nicolas</DIV> <DIV>&nbsp;</DIV> <DIV>&nbsp;</DIV> Tue, 21 Aug 2007 14:52:41 GMT https://ni.lithium.com/t5/Counter-Timer/Signal-modified/m-p/568436#M5253 robinet_l2001 2007-08-21T14:52:41Z https://ni.lithium.com/t5/Counter-Timer/Signal-modified/m-p/570779#M5259 <DIV></DIV>It sounds like PFI9 (CTR0 GATE) is trying to drive the signal as well. Try disabling the PFI9 output in software.<BR /><BR />If that's not the problem, it's possible (though admittedly unlikely) that your square wave has a very high source impedance, so high that it cannot overcome the ~50 kohm pull-up resistor at the PFI9 input.<BR /><BR />Hope this helps,<BR />Ed<BR /><BR /><DIV></DIV> Sun, 26 Aug 2007 17:12:18 GMT https://ni.lithium.com/t5/Counter-Timer/Signal-modified/m-p/570779#M5259 EBL 2007-08-26T17:12:18Z