NI USB 8452 How to enable Vref I/O Reference Voltage

[gogs909]

Hi All

In LabView where do I find the control to enable / turn on the Vref output of the 8452 ( pin 1 of IDE-40 connector)

I am using the 8452 to send / receive data from D/A and A/D devices over SPI.

Devices are 4 off MCP4922 and a MCP3008.

Data exchange between 8452 and these devices is all good under LabView.

My plan is to use the 8452 Vref instead of Vcc as the reference for the D/A devices.

many thanks.

[AJost]

Hi Gogs,

I don't have a 8452 at hand so I can't try out my suggestions myself.

The manual says: 

Note Vref is not enabled before you choose a specific voltage or use the default voltage
(3.3 V). While the device is in USB suspend, this output is disabled.

It is not completely clear where to set this voltage (and keep in mind I can't try it out), but I would suggest to try a 8452 property node to set the IoVoltLevel.

Andreas

[gogs909]

Hi Andreas

thanks for the reply to my initial post.

The manual page 3-12 shows a block diagram of the 8452. It looks like the programmable Voltage drives the Vref and the FPGA so I am guessing they have to be at the same voltage.  I wanted to set a different Vref out on pin 1 to use with the external D/A and A/D chips. I have solved this with another reference voltage on my circuit board.

I used the example "General SPI Read" which includes the NI-845x Property Node and specifically sets IoVoltLevel but still no output at pin 1.

It would be nice to know why, but I have a work around.

many thanks.