MRF39RA Datasheet, PDF (39/72 Pages) Microchip Technology – Low-Power, Integrated UHF Receiver

MRF39RA
4.5.6.4 CRC-Based
The CRC check is enabled by setting bit CrcOn in
RegPacketConfig1. It is used for checking the integrity
of the message. The checksum is calculated on the
received payload and compared with the two
checksum bytes received. The result of the comparison
is stored in bit CrcOk.
By default if the CRC check fails then the FIFO is
automatically cleared and no interrupt is generated.
This filtering function can be disabled via
CrcAutoClearOff bit and in this case, even if CRC fails,
the FIFO is not cleared and only PayloadReady
interrupt goes high. Note that in both cases, the two
CRC checksum bytes are stripped off by the packet
handler and only the payload is made available in the
FIFO.
The CRC is based on the CCITT polynomial, see
Figure 4-12. This implementation also detects errors
due to leading and trailing zeros.
FIGURE 4-12:
CRC IMPLEMENTATION
data in pu t
CRC Po lyn om i al = X¹⁶ + X¹² + X⁵ + 1
X¹⁵
X ¹⁴
X ¹³
X ¹²
X¹¹
** *
X⁵
X⁴
* **
X⁰
 2015 Microchip Technology Inc.
DS40001778B-page 39