SBAS683B August 2014 – May 2020 ADS1120-Q1
PRODUCTION DATA.
The following list shows a pseudo code sequence with the required steps to set up the device and the microcontroller that interfaces to the ADC in order to take subsequent readings from the ADS1120-Q1 in continuous-conversion mode. The dedicated DRDY pin is used to indicate availability of new conversion data. The default configuration register settings are changed to gain = 16, continuous-conversion mode, and simultaneous 50-Hz and 60-Hz rejection.
Power-up;
Delay to allow power supplies to settle and power-up reset to complete; minimum of 50 µs;
Configure the SPI interface of the microcontroller to SPI mode 1 (CPOL = 0, CPHA = 1);
If the CS pin is not tied low permanently, configure the microcontroller GPIO connected to CS as an output;
Configure the microcontroller GPIO connected to the DRDY pin as a falling edge triggered interrupt input;
Set CS to the device low;
Delay for a minimum of td(CSSC);
Send the RESET command (06h) to make sure the device is properly reset after power-up;
Delay for a minimum of 50 µs + 32 · t(CLK);
Write the respective register configuration with the WREG command (43h, 08h, 04h, 10h, and 00h);
As an optional sanity check, read back all configuration registers with the RREG command (23h);
Send the START/SYNC command (08h) to start converting in continuous-conversion mode;
Delay for a minimum of td(SCCS);
Clear CS to high (resets the serial interface);
Loop
{
Wait for DRDY to transition low;
Take CS low;
Delay for a minimum of td(CSSC);
Send 16 SCLK rising edges to read out conversion data on DOUT/DRDY;
Delay for a minimum of td(SCCS);
Clear CS to high;
}
Take CS low;
Delay for a minimum of td(CSSC);
Send the POWERDOWN command (02h) to stop conversions and put the device in power-down mode;
Delay for a minimum of td(SCCS);
Clear CS to high;
TI recommends running an offset calibration before performing any measurements or when changing the gain of the PGA. The internal offset of the device can, for example, be measured by shorting the inputs to mid-supply (MUX[3:1] = 1110). The microcontroller then takes multiple readings from the device with the inputs shorted and stores the average value in the microcontroller memory. When measuring the sensor signal, the microcontroller then subtracts the stored offset value from each device reading to obtain an offset compensated result. Note that the offset can be either positive or negative in value.