ADS1118: Application issue.

Hi Reed,

Let me answer you directly and then talk generally about the ADS1118. In short, for 90% of use cases, the single shot mode is the recommended mode of operation.

Reed said:

1. Does CS PIN always need to be set to low in continuous mode? Or is it only set to high when the SPI is used to read data?

Set the CS pin low when you want to send a SPI command and collect the data after the DRDY transition. It does not need to be held low for continuous mode.

Reed said:

2. In continuous mode, if CS signal is high, will ADC continue to automatically sample?

Yes. CS only pertains to SPI transactions and doesn't control conversion start.

Reed said:

3. How to implement 16bit transmission mode in continuous mode?

Essentially, the device doesn't know if you are in 32 bit transmission or 16 bit transmission until the 16th SCLK. After that, the device either waits for the next SCLK transition (32 bit mode) or waits for CS to go high, then it will be configured in 16 bit mode. Again, the conversion doesn't matter.

Reed said:

4. Is there an example program in continuous mode?

Unfortunately, there is not and there isn't any for single shot either. The last time we spoke, I showed the example code and I believe the example code expects the user to code their own SPI frame.

General comments about single shot versus continuous :

In most ADCs it is smart to put the device in continuous mode. However, the ADS1118 rereads the CONFIG register every time data is collected. In other words, every time you grab data from the device, you still need to write the CONFIG MSB and LSB on DIN. 

Most customers choose the ADS1x18 family over the ADS1x15 because of the integrated temperature sensor which means the CONFIG needs to be changed either every cycle or every other cycle. This arbitrarily defines a strict timing in continuous mode, whereas you can still achieve the same data rate in single shot mode if you don't delay after DRDY toggles.

The only time I recommend using continuous, if the ADC should collect data from power up to power down of the system with no pauses or waiting, and the internal temperature sensor is not important for the system.

Hope this helps.

Best,

-Cole