PIC24FJ128GB MICROCHIP [Microchip Technology], PIC24FJ128GB Datasheet - Page 247

• Manufacturer Part Number: PIC24FJ128GB
• Description: 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)
• Manufacturer: MICROCHIP [Microchip Technology]

20.0
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
(CRCXOR<15:1>)
(CRCCON<3:0>), respectively.
FIGURE 20-1:
© 2008 Microchip Technology Inc.
Note:
D
PLEN<3:0>
OUT
be
XOR
PROGRAMMABLE CYCLIC
REDUNDANCY CHECK (CRC)
GENERATOR
programmed
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
and
0
Family
CRC SHIFTER DETAILS
using
the
X1
Reference
0
1
PLEN3:PLEN0
the
IN
p_clk
Hold
BIT 1
X15:X1
OUT
Manual”,
1
PIC24FJ256GB110 FAMILY
Preliminary
bits
bits
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 20-1.
TABLE 20-1:
Note that for the value of X15:X1, 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 20-2.
IN
PLEN3:PLEN0
p_clk
Hold
BIT 2
OUT
Bit Name
X15:X1
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
OUT
DS39897B-page 245
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