To access a specific register from the ADS111x-Q1, the controller must first write an appropriate value to register address pointer bits P[1:0] in the Address Pointer register. The Address Pointer register is written to directly after the target address byte, low R/W bit, and a successful target acknowledgment. After the Address Pointer register is written, the target acknowledges, and the controller issues a STOP or a repeated START condition.

When reading from the ADS111x-Q1, the previous value written to bits P[1:0] determines the register that is read. To change which register is read, a new value must be written to P[1:0]. To write a new value to P[1:0], the controller issues a target address byte with the R/W bit low, followed by the Address Pointer register byte. No additional data has to be transmitted, and a STOP condition can be issued by the controller. The controller can now issue a START condition and send the target address byte with the R/W bit high to begin the read. Figure 8-9 details this sequence. If repeated reads from the same register are desired, there is no need to continually send the Address Pointer register, because the ADS111x-Q1 store the value of P[1:0] until modified by a write operation. However, for every write operation, the Address Pointer register must be written with the appropriate values.