PIC24FJ16GA MICROCHIP [Microchip Technology], PIC24FJ16GA Datasheet - Page 181

• Manufacturer Part Number: PIC24FJ16GA
• Description: 28/44-Pin General Purpose, 16-Bit Flash Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

19.0
The programmable CRC generator offers the following
features:
• User-programmable polynomial CRC equation
• Interrupt output
• Data FIFO
The module implements a software configurable CRC
generator. The terms of the polynomial and its length
can be programmed using the CRCXOR (X<15:1>) bits
and the CRCCON (PLEN3:PLEN0) bits, respectively.
FIGURE 19-1:
© 2008 Microchip Technology Inc.
Note:
D
PLEN<3:0>
OUT
XOR
PROGRAMMABLE CYCLIC
REDUNDANCY CHECK (CRC)
GENERATOR
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
”Section 30. Programmable Cyclic
Redundancy Check (CRC)” (DS39714).
IN
p_clk
Hold
BIT 0
OUT
0
Family
CRC SHIFTER DETAILS
X1
Reference
0
1
IN
p_clk
Hold
BIT 1
OUT
Manual”,
1
PIC24FJ64GA004 FAMILY
Preliminary
CRC Shift Register
X2
0
1
CRC Write Bus
Consider the CRC equation:
To program this polynomial into the CRC generator,
the CRC register bits should be set as shown in
Table 19-1.
TABLE 19-1:
Note that for the value of X<15:1>, the 12th bit and the
5th bit are set to ‘1’, as required by the equation. The 0
bit required by the equation is always XORed. For a
16-bit polynomial, the 16th bit is also always assumed
to be XORed; therefore, the X<15:1> bits do not have
the 0 bit or the 16th bit.
The topology of a standard CRC generator is shown in
Figure 19-2.
IN
PLEN3:PLEN0
p_clk
Hold
BIT 2
OUT
Bit Name
X<15:1>
2
CRC Read Bus
EXAMPLE CRC SETUP
X3
x
0
1
16
+ x
X15
12
000100000010000
0
1
+ x
5
Bit Value
+ 1
IN
BIT 15
p_clk
1111
Hold
DS39881C-page 179
OUT
15