USB-6501 output structure

[TonyMerolla]

Figure 4 of the NI USB-6501 OEM User Guide shows a port IO circuit.  Rp is populated with a 4.7 kOhm pull up resistor.  The documentation states an output can be configured as push-pull.  Does that indicate that actual micropin on the USB microcontroller, as shown in Figure 3 block diagram, will be configured as push-pull, basically overriding the pull up / open drain circuit?  Is there circuit diagram of what an actual port pad looks like?  That is, when push-pull, does the port pad have a dual transistor circuit connected to it?  

Reviewing the PCB, I observe a low side transistor on all the pins with the 4.7 kOhm pull up resistor, Rp.

Thank you. 

[RoxtheFox]

Hi Tony,

You have to software configure your digital output port so that it becomes a push-pull output. To do this, there are several ways outlined in this KB:

http://digital.ni.com/public.nsf/allkb/D9B4018C3E540CE4862570F30068C0DB?OpenDocument 

This forum post also highlights how you can change the output type in software:

http://forums.ni.com/t5/Multifunction-DAQ/USB-6501-DIO-Push-Pull-Configuration/td-p/1151965 

Once you set this, the DAQ device will automatically change its settings in order to operate as a push- pull device. No, there is not an explicit circuit drawing of the proprietary hardware for the port pad. Figure 5 of the manual shows the basic port configuration for the different output types. 

[TonyMerolla]

Hi Roxana.  Thank you  for the information.  When I try the links you provide, they do not work.  Maybe I am doing something in error when I try to execute them.

A question regarding your statement below regarding the port pin circuit.  Acknowledged you can not show the circuit detail.  However, based on Fig  6 of the User's Guide (you state this below), the port is open drain with the pull up resistor.  Hence a change in software then reconfigures the port pin to actually have the structure of a push pull transistor circuit?  I'm trying to wrap my head around the pull up resistor now in parallel with high side FET (I suspect).  As I look at the board I see a low side transistor and the 4.7 kohm resistor.  I am thinking about the output of the microcontroller connected to that circuit.

Thank you.

tony 

[Daniel.Parrott]

Hi Tony,

This link should work. I've added the title so you can at least search it as well

How Do I Configure My NI Device to Be Open-Drain (Open Collector) or Push-Pull (Active Drive)?: http://digital.ni.com/public.nsf/websearch/D9B4018C3E540CE4862570F30068C0DB?OpenDocument

Title of Forum: 

• NI Discussion Forums
• :
• Most Active Hardware Boards
• :
• Multifunction DAQ
• :
• USB-6501 DIO Push Pull Configuration

http://forums.ni.com/t5/Multifunction-DAQ/USB-6501-DIO-Push-Pull-Configuration/td-p/1151965

I can try and gather more info on what exactly the software does when we're configuring the push-pull configuration. 

[Daniel.Parrott]

Hi Tony,

It looks like you may have found a documentation issue. We're still trying to pursue this to get to the bottom of it, but I'll let you know once we do!

[TonyMerolla]

Hello,

Thank you for the information.  The link to the note works.  The basis of my original question is to understand correctly this output structure of the USB-6501; hence, apply the part correctly.

[Daniel.Parrott]

Hi Tony,

I did get some clarification on this. In Figure 6 of the 6501 User Manual the circuit depicted acts like an open drain and will weakly pull up to 5V. When the Push/Pull configuration is configured, the DAQmx driver basically adds another resistor into the circuit that drives the voltage. Unfortunately that's as much info as I can provide, but I hope that helps!

[TonyMerolla]

Interesting.  Thanks for digging into this.  Not how I think of push-pull, but all info is good info.  My application I bufffer the USB-6501 digital out as a conservative approach to the design.

Regards,

tony