Accessing a specific register on the INA700 is accomplished by writing the appropriate value to the register pointer. See Register MapsRegister MapsRegister Maps for a complete list of registers and corresponding addresses. The value for the register pointer (as shown in Figure 7-13) is the first byte transferred after the secondary device address byte with the R/W bit low. Every write operation to the device requires a value for the register pointer.

Writing to a register begins with the first byte transmitted by the main device. This byte is the secondary device address, with the R/W bit low. The device then acknowledges receipt of a valid address. The next byte transmitted by the main device is the address of the register to be accessed. This register address value updates the register pointer to the desired internal device register. The next two bytes are written to the register addressed by the register pointer. The device acknowledges receipt of each data byte. The main device can end data transfer by generating a start or stop condition.

When reading from the device, the last value stored in the register pointer by a write operation determines which register is read during a read operation. To change the register pointer for a read operation, a new value must be written to the register pointer. This write is accomplished by issuing a secondary device address byte with the R/W bit low, followed by the register pointer byte. No additional data are required. The main device then generates a start condition and sends the address byte for the secondary device with the R/W bit high to initiate the read command. The next byte is transmitted by the secondary device and is the most significant byte of the register indicated by the register pointer. This byte is followed by an Acknowledge from the main device; then the secondary device transmits the least significant byte (LSB). The main device may or may not acknowledge receipt of the second data byte. The main device can end the data transfer by generating a Not-Acknowledge after receiving any data byte, or generating a start or stop condition. Continually sending the register pointer bytes is not necessary if repeated reads from the same register are desired. The device retains the register pointer value until the value is changed by the next write operation.

Figure 7-11 shows the write operation timing diagram. Figure 7-12 shows the read operation timing diagram. The following diagrams show reading and writing to 16-bit registers.

Register bytes are sent by most significant byte first, followed by the least significant byte.

A. The value of the Secondary Device Address byte is determined by the settings of the A0 address pin. See Table 7-2.

B. The device does not support packet error checking (PEC) or perform clock stretching.

Figure 7-11 Timing Diagram for Write Word Format

A. The value of the Secondary Device Address byte is determined by the settings of the A0 address pin. See Table 7-2.

B. Read data is from the last register pointer location. If a new register is desired, the register pointer must be updated. See Figure 7-13.

C. ACK by the main device can also be sent.

D. The device does not support packet error checking (PEC) or perform clock stretching.

Figure 7-12 Timing Diagram for Read Word Format

A. The value of the Secondary Device Address Byte is determined by the settings of the A0 address pin. See Table 7-2.

Figure 7-13 Typical Register Pointer Set