Hey guys,
I'm trying to figure out why my DRDY signal on my ADS1299 is always just half of the desired frequency (in RDATAC mode). For example, if I set DR[2:0]=101 in the CONFIG1 register (=500SPS), the DRDY signal has a frequency of 250Hz. I don't know if I completely misunderstand something here, but let me show you what I got:
This is a oscilloscope screen capture from the START (yellow) and DRDY (blue) signals. It shows the 8ms settling time after START goes high, which is correct as stated on p. 29 of the datasheet (remember, for DR[2:0]=101).
Now, t_DR should be 1/500=2ms, but the next screen shows it's 4ms, so the frequency is only 250Hz.
The following screenshots were made with DR[2:0]=110, which should be 250Hz, but same effect as before, it's just 125Hz. The yellow waveform shows SCLK (27 bytes each) and blue shows DRDY.
The following screen is a closeup. In the previous picture it looks like the DRDY signal is a perfect square wave, but in fact the rising edge looks like this:
It's a 2us wide pulse and after another 3us it goes high (which is the positive half wave of the previous picture). As stated on p. 29 of the datasheet, this first pulse is correct, it should be 4/f_clk wide, which is 2us (f_clk = 2.048MHz).
So there are two things that are in question:
1) why is the frequency of DRDY only half of the set conversion rate?
2) is it ok that DRDY goes high after that 2us pulse and 3us pause? According to fig. 36 on p. 30 in the datasheet it should only be that 2us pulse.
Thanks for your help in advance,
Andreas
