DSPIC33FJ32GP302THSLASHSP datasheet(287/403 Pages) MICROCHIP

287 / 403 page

 2009 Microchip Technology Inc.

Preliminary

DS70292D-page 287

dsPIC33FJ32GP302/304, dsPIC33FJ64GPX02/X04, AND dsPIC33FJ128GPX02/X04

25.0

PROGRAMMABLE CYCLIC

REDUNDANCY CHECK (CRC)

GENERATOR

The programmable CRC generator offers the following

features:

• User-programmable polynomial CRC equation

• Interrupt output

• Data FIFO

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

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

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.

FIGURE 25-1:

CRC SHIFTER DETAILS

Note 1: This data sheet summarizes the features

the

dsPIC33FJ32GP302/304,

dsPIC33FJ64GPX02/X04,

and

dsPIC33FJ128GPX02/X04

families

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.

Bit Name

Bit Value

PLEN<3:0>

1111

X<15:1>

000100000010000

OUT

BIT 0

p_clk

OUT

BIT 1

p_clk

OUT

BIT 2

p_clk

OUT

BIT 15

p_clk

X15

XOR

DOUT

PLEN<3:0>

Hold

CRC Read Bus

CRC Write Bus

CRC Shift Register

DSPIC33FJ32GP302TH/SP Datasheet(PDF) 287 Page - Microchip Technology

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