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ads1298 pacemaker detection

Eckart Hanl
Intellectual 290 points
Other Parts Discussed in Thread: ADS1298

Hello,

i have a problem with the pacemaker detection with the hardware use. I will detect a pacemaker signal with the two pins TESTP_PACE_OUT1 and TESTN_PACE_OUT2. So i connect the two pins with my microcontroller and now i don´t know what happens with this two lines. I read the datasheet and the part with the pace detect on page 68 but i don´t understand the working. When the ads1298 detect a pacemaker signal is there a high signal on the TESTP_PACE_OUT1 or TESTN_PACE_OUT2 pin? And with this high signal i can read it as an input with my controller? Can you explain me how the External Hardware Approach works?

In may datasheet of the ads1298 i can read the following lines:

"The output of the PACE detection logic can then be fed into the device through one of the GPIO pins. The GPIO data are transmitted through the SPI port and loaded 2tCLKs before DRDY goes low."

Can you explain what it mean? Have i to connect a GPIO Pin with my controller and then how can i read the GPIO data through the SPI? Is there an interrupt like the DRDY pin?

The register setting of my PACE Detect Register is 0000 0001. So the channel1 is for TESTP_PACE_OUT1and channel2 is for TESTN_PACE_OUT2 and the PACE detect buffer turned on.

I hope you can help me.

  • 0
    TI__Guru**** 174600 points

    Hi Eckart,

    Take a look at Figure 64 (page 69) of the current ADS1298 data sheet.  The TESTx_PACE_OUT signals are buffered output from the internal PGA.  The hardware pace detection circuitry is basically a comparator circuit.  When using the ADS1298 with hardware pace detection, you would have this comparator circuit fed by the output signals of the TESTx_PACE_OUT.  The output pulse you receive from the comparator then is fed back into a GPIO on the ADS1298.  The status (absence or presence) of the pulse would then be part of the 24-bit status word you get from the ADS1298. 

    Looking at Figure 37 (page 32), you can see how the data from the ADS1298 is organized on the SPI bus.  The first data accessed from the ADS1298 output is STATUS - this data is formatted with the four MSBs fixed at 1100 followed by the lead off status bits and the GPIO status bits.

     

  • 0 in reply to Tom Hendrick
    Intellectual 290 points

    Hello Hendrik,

    thank you for your fast answer. I have read out the GPIO status of the first 24 bit status word. But nothing changed when i try it with a peace maker signal with my ECG simulator. The GPIO status is the same like with a normal sinus rhythm. The last four bits are for the GPIO1-GPIO4. Which bit changes when a peace maker is detected? Is it the GPIO1like it is shown in figure 64? How must to be my register settings for the GPIO register and the PACE detect register? Must i have to connect the TESTx_PACE_OUT pins with my controller to read the GPIO status and to use the hardware pace detection or does it also works without this two lines connected?.

    Best Regards

    Eckart

  • 0 in reply to Eckart Hanl
    TI__Guru**** 174600 points

    Hi Eckart,

    The signal that you see on the ADS1298 TESTx_PACE_OUT will be an analog signal gained by the PGA stage.  Being an analog signal, you cannot simply tie that into your processor unless it happens to have an integrated amplifier.  You need to take the TESTx_PACE_OUT through an external gain and comparator stage in order to isolate and detect the pace maker pulse (2mV-700mV in amplitude, pulse width of 0.1ms to 100ms).  Once you isolate and detect the pace pulse, you feed that logic signal back into the GPIO pin of the ADS1298.