Datasheet

 2010 Microchip Technology Inc. DS39940D-page 253
PIC24FJ64GB004 FAMILY
21.0 32-BIT PROGRAMMABLE
CYCLIC REDUNDANCY CHECK
(CRC) GENERATOR
The programmable CRC generator provides a
hardware-implemented method of quickly generating
checksums for various networking and security
applications. It offers the following features:
• User-programmable CRC polynomial equation,
up to 32 bits
• Programmable shift direction (little or big-endian)
• Independent data and polynomial lengths
• Configurable Interrupt output
• Data FIFO
A simplified block diagram of the CRC generator is
shown in Figure 21-1. A simple version of the CRC shift
engine is shown in Figure 21-2.
FIGURE 21-1: CRC BLOCK DIAGRAM
FIGURE 21-2: CRC SHIFT ENGINE DETAIL
Note: This data sheet summarizes the features
of this group of PIC24F devices. It is not
intended to be a comprehensive reference
source. For more information, refer to the
“PIC24F Family Reference Manual”,
Section 41. “32-Bit Programmable
Cyclic Redundancy Check (CRC)”
(DS39729).
Variable FIFO
(4x32, 8x16 or 16x8)
CRCDATH
CRCDATL
Shift Buffer
CRC Shift Engine
CRCWDATH CRCWDATL
LENDIAN
10
CRCISEL
1
0
FIFO Empty Event
Shift Complete Event
Set CRCIF
2 * FCY Shift Clock
CRCWDATH CRCWDATL
Bit 0 Bit 1 Bit n
(2)
X(1)
(1)
Read/Write Bus
Shift Buffer
Data
Bit 2
X(2)
(1)
X(n)
(1)
Note 1: Each XOR stage of the shift engine is programmable. See text for details.
2: Polynomial length n is determined by ([PLEN<3:0>] + 1).