The ADS1115 has a 16-bit ADC and therefore puts out 16-bit data conversions. The controller device reads from the conversion register to get the ADC conversion data. The conversion register address pointer is 00h. Conversion data appears as a 16-bit result in binary two’s complement. A positive full-scale input produces an output code of 7FFFh and a negative full-scale input produces an output code of 8000h.

With the ADDR pin connected to GND, the device responds to address 48h. Figure 4-5 shows an example read from the Conversion Data register at the 00h address pointer.

The I²C write begins with a START condition. SDA is pulled low, and then SCL is pulled low. Then the controller writes the I²C address. Again, the device responds to an address of 100 1000 (or 48h).

The controller first needs to tell the device which register is to be read from. For this, the communication first sends an I²C Write to the device so that to set up the read from the Data Conversion register of the ADS1115. At this point, the R/W bit is set low, indicating that the communication begins with a write to the device.

When the address frame is completed, the ADS1115 ACKs the address by pulling down the SDA for the last bit of the address frame.

After indicating that the controller is reading from the ADS1115, the controller tells the device which register is read from. The second byte is the register pointer for the Data Conversion register. Here, send 00h to the ADS1115. As a response, the ADS1115 pulls down on SDA for an ACK. Finally, the controller issues a STOP to release the bus.

Now that the controller has told the device to access the data conversion register, the controller follows up with the read from the register. The controller writes the I²C address again. The controller has already indicated which register is to be read from, now the controller sends a read to the device so that the data conversion register of the ADS1115 can be read. At this point, the R/W bit is then set high, indicating the read. Again, after the completion of the address frame, the ADS1115 ACKs the address.

The next two data bytes are used to read the register. The first byte is the most significant byte of the conversion data and then the second byte follows as a read of the least significant byte conversion data. An ACK from the controller follows each byte controller. Finally, the controller sends a STOP to end the I²C communication.

As in the previous example, Figure 4-5 is a convenient diagram showing the I²C communication with the device. If there are problems in communication, an oscilloscope plot of the SDA and SCL can be used to compare against the this example write.