Opus Temperature Reading

Without a battery the logger functionality doesn't work. But it is possible to make temperature measurements in passive mode. And it is also possible to measure the voltage at the battery pin in passive mode, like a general purpose analog input. 

Temperature can be measured with a Select command to the User bank, bit address: 0xB0 using the following mask:

VFC is the On-Chip RSSI (value between 0 and 31). So a mask of 0x0BE0 will perform a single measurement (no averaging) and allow any value of On-Chip RSSI. Then within the same power session, read word address 0x02 in the User bank for the temperature measurement (bits 0 to 3 are always zero, bits 4 to 15 are the temperature in C expressed as two's complement with four fractional LSBs)

But in order to get a good temperature measurement there has to be at least 3 milliseconds, for every measurement, between the SELECT command that activates the temperature measurement and the READ command. For some readers this is easy, like ThingMagic, by setting the T4 parameter with a delay in microseconds. But without this parameter it is also possible to insert an "artificial delay" using useless SELECT commands. For example using a couple of SELECTS to the TID (E2C24500) may be good enough to create this delay.