dspic33fj128mc204 Microchip Technology Inc., dspic33fj128mc204 Datasheet - Page 307

• Manufacturer Part Number: dspic33fj128mc204
• Description: High-performance, 16-bit Digital Signal Controllers
• Manufacturer: Microchip Technology Inc.

26.0
The programmable CRC generator offers the following
features:
• User-programmable polynomial CRC equation
• Interrupt output
• Data FIFO
FIGURE 26-1:
© 2009 Microchip Technology Inc.
Note:
D
PLEN<3:0>
OUT
XOR
PROGRAMMABLE CYCLIC
REDUNDANCY CHECK (CRC)
GENERATOR
This data sheet summarizes the features
of
dsPIC33FJ64MCX02/X04,
dsPIC33FJ128MCX02/X04
devices. It is not intended to be a
comprehensive reference source. To com-
plement the information in this data sheet,
refer to the “dsPIC33F Family Reference
Manual”, Section 36. “Programmable
Cyclic Redundancy Check (CRC)”,
which is available from the Microchip web-
site (www.microchip.com).
IN
p_clk
Hold
BIT 0
OUT
the
0
CRC SHIFTER DETAILS
dsPIC33FJ32MC302/304,
X1
0
1
IN
p_clk
BIT 1
Hold
families
OUT
1
and
Preliminary
CRC Shift Register
of
X2
0
1
CRC Write Bus
26.1
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 26-1:
To program this polynomial into the CRC generator,
the CRC register bits should be set as shown in
Table 26-1.
TABLE 26-1:
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 26-2.
IN
p_clk
Hold
BIT 2
PLEN<3:0>
OUT
Bit Name
X<15:1>
2
Overview
CRC Read Bus
x
16
EXAMPLE CRC SETUP
X3
0
1
+
CRC EQUATION
x
12
X15
000100000010000
0
1
+
x
5
Bit Value
+
IN
BIT 15
1
1111
p_clk
Hold
DS70291C-page 305
OUT
15