How to convert RSSI value to dBm?

Convert the unsigned raw counts (x) to a signed integer (y).

If x < 127; y = x
If x > 127; y = x - 256

Convert the signed counts (y) to RSSI in dBm, subtract -45 dBm
RSSI = y – 45 dBm

Example:
Raw Counts = 217
Convert to signed integer : 217 – 256 = -39
Calculate RSSI (dBm) : -39 – 45 = -84 dBm