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Generating spi signals from labview's DAQ card to control ADS1298ECG-FE daughter board stand alone

Vivek Ravi
Prodigy 240 points
Other Parts Discussed in Thread: ADS1298, ADS1298ECGFE-PDK

Hey guys,

I have a few questions about the ADS1298 I was hoping somebody could answer.

I tested the ADS1298 hardware with the motherboard provided with the eval board and it works fine. Now, I would like to detach the daughter board from the motherboard and try testing it stand alone. For our application, we don't want to use an external processor to control the ADS1298 at this point. So we were thinking of using labview's signal express to genetare the SPI control signals. Yes, this is not an elegant idea but we just want to check if the device ID can be read by providing SPI commands through labviews DAQ card. I have a few questions regarding this:

a) Has anybody tried this approach of using labview to generate spi signals to the ADS1298 board? If yes, could you please guide me to a link in the e2e forum. I tried looking and didn't find any. Does this sound like a feasible idea to at all or can anybody oversee potential pitfalls?

b) On powerup what is the default value of the conifguration and channel registers? Do the contents get erased on each power up?  I ask because, since the DIN signal I will be providing will be very rigid(in the sense that I'm going to explicitly generate a signal with the opcodes I need to be able to read the device ID) I want to write to as few registers as possible.

c) I read in the ads1298 datasheet that the device attempts to decode and execute commands every eight serial clocks. I would like to know how I can present multiples of 8 SCLK's to the device during each serial transfer? Do I need to use the CS signal in someway for that?

d) After detaching the motherboard from the daughter board, I would like to know what the SPI and power connections need to be made. I read in the e2e forum that TI was working on a video tutorial that shows how to hook up the board to an external processor. Can I have a link to that video?

I would really appreciate someone getting back to me with answers to some of these questions,

regards,
V

  • 0
    TI__Guru**** 176581 points

    Hi Vivek,

    We've not connected the ADS1298 board up to the NI DAQ, but there maybe someone else here on the forum that has.  If all you are attempting to do at the moment is read back the configuration registers, that should not be too difficult to do.

    Table 12 in the data sheet lists the power on reset settings of the various registers in the ADS1298 - everything is 0x00 except for the first four registers.  If you configure the ADS1298 for something other than the defaults, the register contents will revert to the default state with a power cycle.  You can see this to some extent in the ADS1298ECGFE-PDK software.  We give you the option to reset the device to our 'programmed' defaults or to the device 'reset' defaults (those shown in Table 12).

    The /CS input can be held low through multiple command cycles.  In fact, it could be tied low permanently - we don't normally recommend doing that though as it is the only way to reset the serial interface without powering off the device.

    We've not got that video posted yet, but page 66 of the ADS1298ECGFE-PDK Users Guide (schematic sheet 5 of 5) shows the connections associated with J4 - the main power input to the board.  You need +5V and either +3.3 or +1.8 (depends on the position of the shunt on JP24) to properly power the EVM.  Your SPI communication lines would connect to J3. 

  • 0 in reply to Tom Hendrick
    Prodigy 240 points

    Tom,

    Thank you for your response. I really appreciate it. What I was trying to ask in question (c) was, if I can keep my SCLK running continuosly? If I do, will the interface cease because of the extra clock pulses? Do I have to give the device a multiple of 8 SCLK's during a serial transfer? If yes, how would you suggest that I gate the clock for every transfer? Also, with the MMBO motherboard, I probed the SCLK and noticed that it was running at 14MHz for a data rate of 500SPS. Do I have to give it that high a frequency or can I just conform to the min speed as prescribed by the formula in the SPI interface section on page 31 of the ads1298 datasheet?

    regards,

    V

  • 0 in reply to Vivek Ravi
    TI__Guru**** 176581 points

    Hi V,

    You do not have to wait between the application of every eight clock so long as you adhere to the SPI command decode time mentioned in the data sheet.  For example, when reading back the status word and eight channels of data information, you can run a continuous burst of 216 clocks.  If you slow the clock down, you simply need to adhere to the formula mentioned so that you get all data read from the ADS1298 between the DRDY pulses for your given sample rate.