SBOS891B October 2018 – April 2021 TMP144
At power on, the TMP144 operates with a 12-bit temperature output. However, the TMP144 can be programmed to operate in Extended Temperature mode, by setting the ETM bit in the configuration register as '1'. When operating in extended temperature mode, the temperature result and temperature limit registers will be 13-bit instead of 12-bit. This extra bit increases the range of the measurement. As shown in Table 7-1, with a 12-bit temperature, the maximum value is 7FFh or 127.9 °C. With a 13-bit temperature value, however, the maximum value is FFFh or 255.9 °C.
When the extended temperature mode is enabled, the EM bit for the temperature high limit register and temperature low limit registers is usable by the application. TI recommends that the user update the THIGH and TLOW register limits because the added bit will effectively left shift and double the register value. This will double the corresponding temperature limit. However, if the application exits the ETM mode, by changing the bit from 1 to 0, this bit is not cleared. As a result, the limit will be right-shifted by 1 bit and halved unless the register values are updated by the application.
The ETM bit value is considered at the end of every conversion cycle, but the limit registers can be updated immediately after setting the bit to 1.