MCP3913 datasheet(48/82 Pages) MICROCHIP

48 / 82 page

MCP3913

DS20005227A-page 48

 2013 Microchip Technology Inc.

FIGURE 6-9:

Continuous Read Sequences With and Without CRC Checksum Enabled.

The CRC checksum in the MCP3913 device uses the

16-bit CRC-16 ANSI polynomial as defined in the IEEE

802.3 standard: x16 +x15 +x2 +1. This polynomial can

also be noted as 0x8005. CRC-16 detects all single

and double-bit errors, all errors with an odd number of

bits, all burst errors of length 16 or less, and most errors

for longer bursts. This allows an excellent coverage of

the SPI communication errors that can happen in the

system,

and

heavily

reduces

the

risk

miscommunication, even under noisy environments.

The CRC-16 format displayed on the SDO pin depends

on the WIDTH_CRC bit in the STATUSCOM register

(see Figure 6-10). It can be either 16-bit or 32-bit

format, to be compatible with both 16-bit and 32-bit

MCUs. The CRCCOM<15:0> bits calculated by the

MCP3913 device are not dependent on the format (the

device always calculates only a 16-bit CRC checksum).

If a 32-bit MCU is used in the application, it is

recommended

use

32-bit

formats

(WIDTH_CRC = 1) only.

FIGURE 6-10:

CRC Checksum Format.

The CRC calculation computed by the MCP3913

device is fully compatible with CRC hardware

contained in the Direct Memory Access (DMA) of the

PIC24 and PIC32 MCU product lines. The CRC

message that should be considered in the PIC® device

DMA is the concatenation of the read sequence and its

associated checksum. When the DMA CRC hardware

computes this extended message, the resulted

checksum should be 0x0000. Any other result indicates

that a miscommunication has happened and that the

current communication sequence should be stopped

and restarted.

Continuous READ communication without CRC checksum (EN_CRCCOM=0)

Don’t care

SCK

SDI

SDO

Hi-Z

CONTROL

BYTE

16x/24x/32x

Depending on

data format

ADDR

...

ADDR + n

Starts read sequence

at address ADDR

Complete READ sequence

ADDR + 1

16x/24x/32x

Depending on

data format

...

16x/24x/32x

Depending on

data format

16x/24x/32x

Depending on

data format

ADDR

...

Complete READ sequence

ADDR + 1

16x/24x/32x

Depending on

data format

...

16x/24x/32x

Depending on

data format

ADDR + n

Don’t care

ADDR

ADDR + 1

...

ADDR + n

Complete

READ

sequence

Roll-over

ADDRESS SET

Continuous READ communication with CRC checksum (EN_CRCCOM=1)

Don’t care

SCK

SDI

SDO

Hi-Z

CONTROL

BYTE

16x/24x/32x

Depending on

data format

ADDR

...

ADDR + n

Starts read sequence

at address ADDR

Complete READ sequence = Message for CRC Calculation

ADDR + 1

16x/24x/32x

Depending on

data format

...

16x/24x/32x

Depending on

data format

16x/24x/32x

Depending on

data format

ADDR

...

New Message

ADDR + 1

16x/24x/32x

Depending on

data format

...

16x/24x/32x

Depending on

data format

ADDR + n

Don’t care

ADDR

ADDR + 1

...

ADDR + n

Complete

READ

sequence

Roll-over

ADDRESS SET

CRC Checksum

16x or 32x

Depending on

CRC format

16x or 32x

Depending on

CRC format

CRC Checksum

(not part of register map)

New Checksum

Checksum

* n depends on the READ<1:0>

WIDTH_CRC = 0

16-bit format

CRCCOM

<15:8>

CRCCOM

<7:0>

WIDTH_CRC = 1

32-bit format

CRCCOM

<15:8>

CRCCOM

<7:0>

0x00

Note:

The CRC will be generated only at the end

of the selected address set, before the

rollover of the address pointer occurs (see

Figure 6-9).

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