how to read back digital outputs from NI-9403

[jtraw]

We are using a cDAQ-9184 with (2) NI-9403 32 channel digital I/O Module. The modules are being used to control RF switches to route various RF paths as required by our radio test team. I would like to read back the values to verify that at least the output state is correct. A read/verify operation if you will. Is this device capable of allowing such operation, if so, how to go about it.

[Alexander_Sobolev]

I would say that if channel is configured for writing (task active), then you can not read values from it. 

Split wire and make separate read task, but it needs many channels.

Some kind of a multiplexor will allow you to check many channels by using a few digital control channels. Single check during system start to detect shorts or other failure that is not detected by labview (device self-test).

[jtraw]

For digital I/O devices we have two basic types of systems.

A) A digital I/O device that can be configured for either input or output, however the output driver is disconnect from the input receiver when the unit is configured for output. This means the hardware is incapable of reading back any output. This would require that each output bit has a seperate associated recevier to evaluate the signal level from the output. 2 seperate tasks to 2 different sets of digital I/O cards are required to implement read/write verify operation.

B). A digital I/O device that can be configured for either input or output, however the output driver remains connected to the input receiver when the unit is configured for output. In this instance the device internal FW may allow the device to read and write the state of the output. No addtional cards are requried for these type of devices. as the unit can read back the output accordingly.

This raises a couple of questions:

1) Which category does the NI-9403 fall into Digitial I/O type A or B as described above?

2) If the NI-9403 falls into category B and the internal FW allows the ability to read back the digital output. How is this implemented in labVIEW code?

[A_Hint_From_Trent]

Are you just trying to verify thar what you are outputing from a specifc port is correct? 

[jtraw]

Yes, that is correct

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[A_Hint_From_Trent]

If you are using LabVIEW, you can use an indicator on your front panel and connect it to your output channel on the block diagram to monitor what you are outputting. If you're not using LabVIEW, you will need to run the output signal into another channel and monitor it as an input.

[jtraw]

Having an indicator on the front panel will only work If I can can read the ouput to change the state of the indicator. If I can read the output then there is no need for the indicator as I all ready have the information I need without it. That is the place I ma trying to get to.

[A_Hint_From_Trent]

Then we would need to wire two wires from the output and connect one of them to an input pin and read it from there.

[jtraw]

Is that because the NI-9403 is incapable of reading back the output value when configured for write output as described in category "A". If so, this leaves us with the only way to implement this is the additional purchase of cards to read back the output with.

[A_Hint_From_Trent]

Yeah you would either need an additional channel to read in your output or monitor your output using LabVIEW like I mentioned previously. The Bidirectional component just means it can be configured as an input or an output not that it monitors the output port of the channel similar to an SMU.