Digital input behavior question

[Brad_K]

Hi Walter,

"port0" in the device test panel corresponds to the lines that are marked "P0.0" through "P0.7" in the PCI-6143 pinout diagram, not "PFI0" through "PFI9". (In other words, "P0.0" is short for "port0/line0".) The PCI-6143 supports using PFI terminals for timing/triggering signals, but it does not support using PFI terminals for DIO. Your USB-6211 does support using PFI terminals for both timing/triggering signals and DIO, which is why the terminals are labeled "PFI 0/P0.0" in the USB-6211 pinout diagram.

Also, port0 on the PCI-6143 has a weak pull-up resistor on each line, which will cause the lines to read high when they are configured for input and not connected to any external signals.

Brad

[walter-donovan]

My terminology is wrong once again. I am not an electronic engineer. Whatever you call the lines, I have stated that in test panels, if you go to what NI calls digital I/O and hit start after selecting port 0, all lights indicating the individual lines stay high. If there is a slow 5v encoder signal going directly into PFI0 and port 0 is selected to view digital activity, what should you see on the screen?

1) I think you should see bit 0 blinking on and off. Bits 1 through 7 should remain off as there is absolutely nothing attached to them.  

Is this correct? This is the way it worked last week. 

2) This is not what I see. I see 8 lights that come on as soon as I hit "Start". They stay on as I turn the encoder. Not just the one hooked to the encoder but all 8 (7 of which are not attached to anything). Bit 0 light does not blink either.

Is this correct? This is the way it works now. 

I don't know what the distinction is between digital I/O and timing/counting but this encoder is used solely for a reference pulse to trigger analog DA. It has worked in this configuration at speeds up to 5,500 RPMs or   66,000 pulses / second (720 counts / rev).

Message Edited by walter-donovan on 02-10-2009 12:44 PM

[Brad_K · Accepted solution]

Hi Walter,

Behavior #1 is correct for the USB-6211. On the USB-6211, the digital I/O circuits and the counter/timer/trigger circuits are connected to the same pins, which are labeled "PFI0/P0.0" and so on. This is a feature that the PCI-6143 hardware does not have, because the PCI-6143 is based on the older DAQ-STC system timing controller chip and the USB-6211 is based on newer M Series technology.

Behavior #2 is correct for the PCI-6143. On the PCI-6143, the digital I/O circuits are connected to one set of pins, labeled "P0.0" through "P0.7". The counter/timer/trigger circuits are connected to a completely different set of pins, labeled "PFI0" through "PFI9".

In addition, the USB-6211 and PCI-6143 have different digital I/O behavior when nothing is connected to the pin. The PCI-6143 has weak pull-up resistors, which pull floating (i.e. disconnected) digital input pins to the "on" state. The USB-6211 has weak pull-down resistors, which pull floating digital input pins to the "off" state.That is why the USB-6211 displays bits 1-7 as "off" and the PCI-6143 displays bits 0-7 as "on".

On the PCI-6143, if you want to be able to see the encoder in the digital I/O test panel (or in digital I/O tasks in DAQmx), you need to wire it to both "P0.0" and "PFI0". Then you should get similar results to the USB-6211 (except for the behavior of disconnected pins). However, if you only want to use the encoder as an analog input start trigger (or for counter/timer tasks), then you only need to wire it to "PFI0", not "P0.0".

Brad

[walter-donovan]

Thank you Brad for your clear answer. This explained, I have checked the board and it is in fact receiving signals. MAX also seems to be running as intended. That leaves software. That's where we go next.