Hi, Ryan,
Thank you so much for your timely reply. I learned a lot.
Yes, there is a black wire tied to pin 7 of J3 as a /CS sending from the motherboard (TI CC2540). Now I know the configuration of these four signals are right. Thank you.
Do you mean I have to send the START opcode when I power on the ADS1299 EEG-FE? I had thought the chip must have been started working in a RDATAC mode since I can record DRDY signals every 4 ms, which corresponds to the default data rate of 250 SPS.
I did not send the START opcode because I am not very confident with the write register programs I used. For example, if I want to send the command SDATAC to stop the RDATAC mode and change the data rate in CONFIG1 register to 1000 SPS, should I just write 0x11(SDATAC) to the buffer? Is the code below correct?
while(1)
{ CS = CS_ENABLED;
U1CSR &= ~0x02; // Clear transmit byte status.
U1DBUF = 0x11; // Write SDATAC(11h) to stop RDATAC mode.
while(!(U1CSR & 0x02)); // Check if byte is transmitted (and a byte is recieved).
// write CONFIG1 to change date rate to 500 SPS.
U1CSR &= ~0x02;
U1DBUF = 0x41; // WREG Opcode 1---- CONFIG1 address: 01H
while(!(U1CSR & 0x02));
U1CSR &= ~0x02;
U1DBUF = 0x00; // WREG Opcode 2---- No. of register: 1
while(!(U1CSR & 0x02));
U1CSR &= ~0x02;
U1DBUF = 0x94; // Data rate of 1000 SPS
while(!(U1CSR & 0x02));
CS = CS_DISABLED; }
I am sorry for not explaining the amplitude problem of the oscilloscope capture. I should have done that in my last post to save your time.
I am using a very old oscilloscope. It has 4 channels, but I cannot adjust the amplitude of channel 3 and 4. So I use the 10* attenuation in the probes. The DRDY, CS and SCLK should all have an peak amplitude of about 3.3 V, but the DOUT is around 100mV since I didn't get the correct data out. The GND of ADS1299 EEG-FE and the GND of CC2540 and the oscillator are all tied together.
When you are referring to the "a lot of digital feed to the /DRDY and SCLK", you mean the white wires in the PCB figure, right? These most obvious 2 white wires from /DOUT and DOUT pins are connected to channel 1 and 2 of the oscilloscope. Other wises are: SCLK(yellow), /CS(black), DIN(white), DOUT(red), DRDY(blue), just for reference to clear your doubts.
I really appreciate your great help. Thank you very much.