DSPIC33FJ128GP304T-I View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
DSPIC33FJ128GP304T-I Datasheet PDF : 402 Pages
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dsPIC33FJ32GP302/304, dsPIC33FJ64GPX02/X04, AND dsPIC33FJ128GPX02/X04
25.0 PROGRAMMABLE CYCLIC
REDUNDANCY CHECK (CRC)
GENERATOR
Note 1: This data sheet summarizes the features
of the dsPIC33FJ32GP302/304,
dsPIC33FJ64GPX02/X04,
and
dsPIC33FJ128GPX02/X04 families of
devices. It is not intended to be a compre-
hensive reference source. To comple-
ment the information in this data sheet,
refer to “Section 36. Programmable
Cyclic Redundancy Check (CRC)”
(DS70298) of the “dsPIC33F/PIC24H
Family Reference Manual”, which is avail-
able 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 25-1:
CRC SHIFTER DETAILS
25.1 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 25-1: 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 25-1.
TABLE 25-1: 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 25-2.
PLEN<3:0>
0
Hold
XOR
DOUT
OUT
IN
BIT 0
p_clk
1
2
X1
Hold
0
OUT
IN
BIT 1
1
p_clk
CRC Shift Register
X2
Hold
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
DS70292D-page 287
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