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CC1101FIFO is read over the SPI interface, the RXFIFO pointer is not properly updated and thelast read byte is duplicated. To avoid thisproblem one should never empty the RX FIFObefore the last byte of the packet is received.For packet lengths less than 64 bytes it isrecommended to wait until the completepacket has been received before reading it outof the RX FIFO.If the packet length is larger than 64 bytes theMCU must determine how many bytes can beread from the RX FIFO(RXBYTES.NUM_RXBYTES-1) and the followingsoftware routine can be used:1. Read RXBYTES.NUM_RXBYTESrepeatedly at a rate guaranteed to be atleast twice that of which RF bytes arereceived until the same value is returnedtwice; store value in n.2. If n < # of bytes remaining in packet, readn-1 bytes from the RX FIFO.3. Repeat steps 1 and 2 until n = # of bytesremaining in packet.4. Read the remaining bytes from the RXFIFO.The 4-bit FIFOTHR.FIFO_THR setting is usedto program threshold points in the FIFOs.Table 29 lists the 16 FIFO_THR settings andthe corresponding thresholds for the RX andTX FIFOs. The threshold value is coded inopposite directions for the RX FIFO and TXFIFO. This gives equal margin to the overflowand underflow conditions when the thresholdis reached.A signal will assert when the number of bytesin the FIFO is equal to or higher than theprogrammed threshold. This signal can beviewed on the GDO pins (see Table 33 onpage 56).Figure 21 shows the number of bytes in boththe RX FIFO and TX FIFO when the thresholdsignal toggles, in the case of FIFO_THR=13.Figure 20 shows the signal as the respectiveFIFO is filled above the threshold, and thendrained below.NUM_RXBYTESGDONUM_TXBYTESGDO53 54 55 56 57 56 55 54 536 7 8 9 10 9 8 7 6Figure 20: FIFO_THR=13 vs. Number ofBytes in FIFO (GDOx_CFG=0x00 in RX andGDOx_CFG=0x02 in TX)FIFO_THR Bytes in TX FIFO Bytes in RX FIFO0 (0000) 61 41 (0001) 57 82 (0010) 53 123 (0011) 49 164 (0100) 45 205 (0101) 41 246 (0110) 37 287 (0111) 33 328 (1000) 29 369 (1001) 25 4010 (1010) 21 4411 (1011) 17 4812 (1100) 13 5213 (1101) 9 5614 (1110) 5 6015 (1111) 1 64Table 29: FIFO_THR Settings and theCorresponding FIFO Thresholds56 bytesOverflowmarginFIFO_THR=13FIFO_THR=13Underflowmargin8 bytesRXFIFOTXFIFOFigure 21: Example of FIFOs at ThresholdSWRS061C Page 47 of 94