9.5.3 Writing To and Reading From the Registers

To access a specific register from the ADS111x, the master 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 slave address byte, low R/W bit, and a successful slave acknowledgment. After the Address Pointer register is written, the slave acknowledges, and the master issues a STOP or a repeated START condition.

When reading from the ADS111x, 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 master issues a slave 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 master. The master can now issue a START condition and send the slave address byte with the R/W bit high to begin the read. Figure 37 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 store the value of P[1:0] until it is modified by a write operation. However, for every write operation, the Address Pointer register must be written with the appropriate values.

1. The values of A0 and A1 are determined by the ADDR pin.

2. Master can leave SDA high to terminate a single-byte read operation.

3. Master can leave SDA high to terminate a two-byte read operation.

Figure 30. Timing Diagram for Reading From ADS111x

1. The values of A0 and A1 are determined by the ADDR pin.

Figure 31. Timing Diagram for Writing to ADS111x

1. The values of A0 and A1 are determined by the ADDR pin.

Figure 32. Timing Diagram for SMBus Alert Response