The TMP139 provides a default read address pointer mode as shown in Figure 7-8 to read a specific register on the I²C bus. Since the number of bytes to be sent by the host are two less than a standard I²C read operation, this mode provides for a more efficient polling mechanism. The MR18 register, bit DEF_RD_ADDR_POINT_EN is used to enable the mode and bits DEF_RD_ADDR_POINT_Start are used to set the default read address pointer to a specific register in the register map. When enabled, the TMP139 shall set the internal read address pointer to the specific register when there is a Stop condition on the bus.

Figure 7-8 I²C Default Read Address Pointer Mode

There can be two specific cases in this mode of operation. In the first case as shown in Figure 7-9, there is a normal I²C read preceding the default read mode. If a Stop precedes the Start, then the internal read address pointer shall be set to the default address pointer and subsequent data reads shall result in the data bytes sent by the TMP139 corresponding to the default read address pointer. If a Repeated Start is issued instead of a Stop, then the TMP139 shall send data based on the default read address pointer.

Figure 7-9 I²C normal read followed by a Default Read Address

In the second case as shown in Figure 7-10, there is a normal I²C write preceding the default read mode. If there is a Stop, followed by a write bus operation and then a Repeated Start for the read mode, then the TMP139 shall update its internal read address pointer to the default read address and transmit bytes to the host.

Figure 7-10 I²C normal write followed by a Default Read Address