PIC24HJ128GP802-I/ML View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
PIC24HJ128GP802-I/ML Datasheet PDF : 357 Pages
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PIC24HJ32GP302/304, PIC24HJ64GPX02/X04 AND PIC24HJ128GPX02/X04
23.0 PROGRAMMABLE CYCLIC
REDUNDANCY CHECK (CRC)
GENERATOR
Note 1: This data sheet summarizes the features
of
the
PIC24HJ32GP302/304,
PIC24HJ64GPX02/X04
and
PIC24HJ128GPX02/X04 families of
devices. It is not intended to be a
comprehensive reference source. To
complement the information in this data
sheet, refer to Section 36.
“Programmable Cyclic Redundancy
Check (CRC)” (DS70311) of the
“PIC24H Family Reference Manual”,
which is available from the Microchip
website (www.microchip.com).
2: Some registers and associated bits
described in this section may not be avail-
able on all devices. Refer to Section 4.0
“Memory Organization” in this data
sheet for device-specific register and bit
information.
The programmable CRC generator offers the following
features:
• User-programmable polynomial CRC equation
• Interrupt output
• Data FIFO
FIGURE 23-1:
CRC SHIFTER DETAILS
23.1 Overview
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 (PLEN<3:0>) bits, respectively.
EQUATION 23-1: CRC EQUATION
x16 + x12 + x5 + 1
To program this polynomial into the CRC generator,
the CRC register bits should be set as shown in
Table 23-1.
TABLE 23-1: EXAMPLE CRC SETUP
Bit Name
Bit Value
PLEN<3:0>
X<15:1>
1111
000100000010000
For the value of X<15:1>, the 12th bit and the 5th bit are
set to ‘1’, as required by the CRC equation. The 0th bit
required by the CRC 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 0th bit or the 16th bit.
The topology of a standard CRC generator is shown in
Figure 23-2.
PLEN<3:0>
0
Hold
XOR
DOUT
OUT
IN
BIT 0
p_clk
1
2
X1
Hold
CRC Shift Register
X2
Hold
0
OUT
IN
BIT 1
1
p_clk
0
OUT
IN
BIT 2
1
p_clk
15
X3 X15
Hold
0
0
OUT
IN
1
1
BIT 15
p_clk
CRC Read Bus
CRC Write Bus
© 2009 Microchip Technology Inc.
Preliminary
DS70293D-page 249
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