Tool/software: Code Composer Studio
I want to read the external signal through CCS. I have successfully read the internal test square wave as shown in figure 1 below, but when I changed the register to read the external signal 100 HZ SIN wave, the data output figure is as shown in figure 2. What is the reason? How can I improve this result?
Figure 3 shows the results of the external test signal presented on the oscilloscope.
figure 1
figure 2
figure 3
I use bipolar power supply, JP2(1-2), JP20(2-3)
When the external signal is input, do I need to connect the positive and negative ends of the signal generator to the same channel's VINP and VINN? Or connect one channel's VINP to the positive end of the signal generator, and the other channel's VINP to the negative end of the signal generator End, as GND?
Figure 3 is directly connected to the oscilloscope from the signal generator without any circuit in the middle
The following picture shows the jumper settings of ads1299
Image source: modified from TI ads1299 USER GUIDE
After a day of testing, I connected the VINP of channel1 to VINN so that the input signal was 0, and changed the registers config1, config2, config3, cfannel 1 to observe the results. The results are shown in the figure. It should be that the external input signal cannot enter the ADS1299 through the channel's VINP and VINN. No matter whether the signal generator is used to input the 100HZ SIN wave, or the VINP and VINN are connected, the result is the same. I suspect that the register and the jumper on the circuit board are set. The cause, but I don’t know yet what caused it.
config1: 0x96
config2: 0xC0
config3: 0xE0
MISC1: 0x00
channel1: 0x68
I have successfully read the external signal, but encountered a small problem.
The DR[2:0] of the ADS1299 register config1, for example, "110: fMOD / 4096 (250 SPS)" means that each channel has a sampling rate of 250? Or does it mean that the sampling rate of each channel is 250/8 ?
If I only need to use 1 channel and want to close the other channels, can I set the other channels to 0x89 to close it?
I used the signal generator to give a 10HZ sin wave, config1 was set to 0x96, and finally read out a perfect wave pattern.
If I change to a sin wave of 10Hz, but the sampling rate is increased to 1K (config1 is set to 0x94), the result is as shown below.
If I change to a sin wave of 10 Hz, but the sampling rate is increased to 4K (config1 is set to 0x92), the result is as shown below.
But when I try to increase the sin wave to 50Hz,sampling rate is increased to 250 (config1 is set to 0x96), the data becomes as shown below.
Theoretically, the higher the sampling frequency, the more complete the signal should be, but from the picture it seems that this is not the case. And I found that when DR[2:0] is set to 250SPS, there are 10 sin waves among 250 data points; but when DR[2:0] is set to 1k SPS, there are 20 sin waves, I think Should there be only 10 sin waves?
I am thinking to try is not my understanding of DR[2:0] of config1 wrong? I understand him as DR[2:0] is equal to the sampling frequency. If not, what are the possible causes of this situation?
I tried to calculate the minimum required SCLK. I tried to calculate SCLK through the formula in section 9.5.2.2 on page 39 of the datasheet, but I don't know how to get tdr and tclk in the formula.
I read the description of section 9.3 on page 20. tclk is the period of fclk, and fclk = 2.048MHz on page 11, so I think tclk = 1/2.048M ?
Although the tdr is mentioned in chapter 9.3, I still don't know how to get the tdr number I want.
