I do mean Pmod AD2. I purchased a Pmod AD2 so that I can read a higher voltage range than the 1.8 volts of the BBB's onboard analog inputs . I am using the I2C Write VI so that I can configure the AD7991 per page 20 of the datasheet. I understand it is not needed to get the Pmod AD2 to work, as the default is the reading of all four of the AD7991 channels, but I was not sure if D3 (in Table 10) needed to be set (in addition to the jumper on the board) in order to define the reference voltage.
The I2C Read VI reads bytes (Bytes to Read), not bits, so I don't believe that I should have to perform a read 8 times. Once I establish communication to the board, the rest will be on the LabVIEW side.
Again, I believe the issue is with the specific I2C addressing with this particular Pmod/AD7991. See Page 23 of the AD7991. I interpret this to mean that a R/W bit must be included in the end of the address in order to "write to" or "read from" the AD7991. The Pmod documentation states: "Unlike other devices that use I²C, no addresses are associated with these two registers; only the read/write bit at the end of the slave address distinguishes between the two registers." However, drilling down in both I2C Write and Read VIs I quickly reach a function call and therefore cannot tell what the code is doing at that point.
Either I am just missing a key detail or there must be a way to "trick" the I2C Write and Read VIs to work with this Pmod.
The only mention of using the Pmod AD2 with LINX and BBB I found was on BeagleBoard.org (https://beagleboard.org/p/ella-rickerson/beaglebone-black-minisumo-bot-pt-2-8a55b6). But of course, when I downloaded the sample code, I see that the two VIs I believe I need were not included. There is another reference to using I2C with LabVIEW (LINX) on the Instructables web site (https://www.instructables.com/id/How-to-use-I2C-in-LabVIEW/). But no example for the Pmod AD2 was given. However, the author (Sudharsan Sukumar) worked for Digilent at the time. Is he still with Digilent? Maybe he can assist.
BTW, some background on me: I have been programming with LabVIEW since LabVIEW 3.0 and have done many LabVIEW, LabVIEW RT, and LabVIEW FPGA projects over the years as a NI Alliance Member. But the NI hardware has always been kind of pricey for home use/little projects. So I was kind of excited when NI created LINX/MakerHub and Digilent (2014-2016 time frame). However, it just seemed to die after that . So there just seems that a little more support/documentation is needed for us LabVIEW users. For this reason, I plan on uploading all of my projects with the BBB and LINX (and the Pmods) to this and the LabVIEW MakerHub site as I develop them so that other LabVIEW users that purchased one of your Home Computing Kits can have additional support. Time to give back I guess.