RX Length Registers
Address = &h004 (low byte) and &h005 (high byte); read-only access
Low and high bytes of the length of received data awaiting readout from the RX data buffer. The Tibbit sets these registers automatically, upon the completion of the IR data recording.
Note that the data length is expressed in bytes (even though the logical unit of data in the RX buffer is a 16-bit word).