I am using a CVI/LabWindows setup to access a DUT using a SPI serial interface. I am using the NI USB-8452 controller to communicate over the serial interface. Due to the inherent long delays between signal edges in the standard SPI communication, I have switched to SPI Stream API mode. This has allowed me to configure the timing edges to desired values between the standard SPI I/O. The 8452 is the master and is driving CS/SCLK/MOSI while getting MISO back from the DUT.
I am using this mode successfully, but now I want to configure the data being sent to the slave in a particular manner, and I haven’t figured out a way to do this with the streaming commands available to me. I have attached a timing diagram from the NI-845x Hardware and Software Manual, which shows the various signals and the timing parameters available.
I am trying to find a way to change the data that is contained in the first “nBits” packet to a different set of data for the second “nBits” packet. I would like to alternate between the data sets, with just the definable T9 timing parameter (CS inactive) separating the packets. If I drive these out as separate packets, I get a 3.5ms delay between packets, which is not allowing me to sample quickly enough. I do, however, need an inactive CS between the alternating packets, so I can’t just lump them all into one “nBits” packet.
I have set NumBits, NumSamples, and MosiData to values that I hoped would work. I have tried different variations of them. I can get the first 6 bytes of MosiData repeating over and over again, with an inactive CS between packets, but I can’t get the second set of 6 bytes to come out on alternating packets. For this scenario, I set NumBits to 48 (8 bits * 6 bytes), NumSamples to 4 (just to see if the alternating pattern would repeat), and MosiData to a large array of data containing the same 12 bytes repeated multiple times.
It seems I have to set up all parameters and then perform StreamStart, StreamRead, and StreamStop. I haven’t been successful trying to change the parameters between StreamStart and SteamStop (e.g. doing a StreamRead, change parameters, then doing another StreamRead).
BTW, if there is another way to accomplish this, please let me know also.
Thanks!