ADS1298 - No DIN nor DOUT data

Juan Rizzato

Other Parts Discussed in Thread: ADS1298

Hello,

I want to interface to the ADS1298 in an university project and i am not getting anything from DOUT nor DIN. These are my specifications:

uC -> 4MHz crystal input to 48MHz with PLL

ADS1298 -> 250SPS

LOW_POWER

                        nCS = 0 -> chip select low
            nPowerDown   =   1
nReset       =   1
      delay 1 second
nReset   =   0
    delay 1 us
nReset   =   1
delay 10 us
      Start   =   1;
   delay 18 ms

   aux = SSP2BUF;
   SSP2BUF = SDATAC; // 0x11; // SDATAC
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0x41; // WREG 01h
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0x03; // register to write: 3
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00100110; // low power 250hz
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010100;
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b11000000;
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;

    SSP2BUF = 0x45; // WREG 05h
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0x08; // registers to write: 8 (gain)
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 1
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 2
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 3
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 4
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 5
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 6
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 7
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 8
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;

   SSP2BUF = 0x10; // Enable RDATAC mode
    while(!SSP2STATbits.BF);
   aux = SSP2BUF;

    delay
   nCS = 1;

Here are some screeen shots flom de oscilloscope:

There you can see the data ready signal (red). i interrupt the micro in the falling edge. Below, the clock signal (yellow) from the SPI module.

Here yo can see in red the clock signal and in yellow the chip select signal. I set it low duting the transmition.

And finally the DIN (red) and DOUT (yellow). Nothing comes in nor out of the spi module.

Do you have any suggestion?

What could be causing not to have anything in DIN or DOUT?

Does DIN and DOUT need any pull up resistors?

Am i missing anything?

Thanks in advance!!!

over 11 years ago

0 Bernhard Wandernoth over 11 years ago

Prodigy 160 points

Hi Juan,

I think the problem is how you set the registers. If you want to write n registers, you need to send n-1 as parameter.
See comment (2) under table 11 on page 37 in the datasheet. I suppose that will solve the problem ;-)

a general note: pease note that the CS/ does not totally disable the SPI interface of the ADS1298. So, the SPI bus is not a real bus. This only matters if you use more than one device at this bus. That said, note the minimum timing requirements, for instance the 17us you need to wait from pulling CS/ low to the first clock pulse. Maybe its better to keep CS/ low the whole time for testing.

DIN is an input. It needs to be held low while reading data, unless you want to write a command or data to the chip while reading at the same time.

Best,

Bernhard

0 Juan Rizzato over 11 years ago in reply to Bernhard Wandernoth

Prodigy 70 points

Thak you very much for your answer. The problem i was getting was a hardware problem so thats why i was not getting any output but your observations were very good =). Now i held CS always low and i modified the configuration registers. Do you mean something like this:

aux = SSP2BUF;
   SSP2BUF = SDATAC; // 0x11; // SDATAC
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0x41; // WREG 01h
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0x02; // 3 registers
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00100110; // LP @250hz
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010100;
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b11000000;
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;

   // Configuracion de ganancias

   SSP2BUF = 0x45; // WREG 05h
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0x07; // 8 registers
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 1
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 2
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 3
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 4
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 5
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 6
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 7
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;
   SSP2BUF = 0b00010000; // Canal 8
   while(!SSP2STATbits.BF);
   aux = SSP2BUF;

Thanks in advance!!

Juan

0 Bernhard Wandernoth over 11 years ago in reply to Juan Rizzato

Prodigy 160 points

Hi Juan,

yes, this should work! At least this register setting will work now. I was stuck in exactly the same problem for days, until a person from TI pointed me to that n-1 problem ;-)

Bernhard

0 Juan Rizzato over 11 years ago in reply to Bernhard Wandernoth

Prodigy 70 points

Thanks for the answer =).

Do the registers configures even if there is something wrong with the DOUT line? I still can not see DOUT. I thought the problem was the hardware but i still not seen DOUT.

Due the fact that I am seeing DRDY and the SPI clock, what else should I test? or what other configuration should I try?

Thanks in advance!!

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ADS1298 - No DIN nor DOUT data