Obtaining a TTL input signal via DIO lines of 7334

[malkoba]

Hi

How can I obtain a TTl input signal from a source via the DIO lines of the 7334 .

Thanks

Mal

[Buechsenschuetz]

I do not quite understand your question.

If you want to know what kind of signal a DIO line will detect properly: the signal has to be less than 0.8V to detect a low state and more than 2.0V to detect a high state. This is compatible with outputs of all TTL logic circuits.

If you have some other circuitry (source) with different specifications for the digital signal you can simply connect a switching transistor in open collector circuit. The DIO lines have pull-up resistors, and when the transistor is switched the DIO input will be tied to less than 0.8V (low level).

Anyhow, if the high output level of your source is more than 5V (there are many control systems with 24V output level) it is better to use galvanic isolation to avoid damage of the motor controller. You can use a relay, or better an opto-isolator. You have to design the series resistor of the opto-isolator such that the input gets proper current to drive the LED (usually 10mA will be sufficient for most optocouplers). If the opto-isolator has an open collector output configuration it can be connected directly to the 7344 DIO line.

Of course you always have to provide a common GND connection between the 7344 board and your signal source (or the open-collector transistor in case you use this configuration or an opto-isolator).

[malkoba]

Hi

Thanks. But what I want to know is how can you use the DIO lines to take an input signal. The example library has two examples (for motion controller DIO) to output a signal but none on how to take an input. I require to get an a certain feedback signal from my external system into my labview programme to do certain processing action in the programme. I  Appreciate your help and advice.

Thanks

Mal

[Jochen]

Malkoba,

here is an example for reading a digital port. As I don't know the LabVIEW version you are using I haven't attached the vi but only a screenshot. Please note that Set I/O Port Direction.flx should only be called once after the program is started so you should execute it outside your program's main loop.



Best regards,

Jochen Klier
National Instruments Germany

Message Edited by Jochen on 11-21-2006 10:07 AM

[malkoba]

Hi

Thanks for the help and advice. I think I will be able to get the signal now.

Thanks

Mal