Microchip Technology DsPIC33 series Manuale utente

2018 Microchip Technology Inc. DS70005340A-page 1

HIGHLIGHTS

This section of the manual contains the following major topics:

1.0 Introduction ....................................................................................................................... 2

2.0 CAN FD Message Frames................................................................................................ 5

3.0 Control Registers .............................................................................................................. 9

4.0 Modes of Operation ........................................................................................................ 51

5.0 Configuration................................................................................................................... 57

6.0 Message Transmission ................................................................................................... 67

7.0 Transmit Event FIFO – TEF ............................................................................................ 76

8.0 Message Filtering............................................................................................................81

9.0 Message Reception ........................................................................................................ 86

10.0 FIFO Behavior................................................................................................................. 92

11.0 Timestamping................................................................................................................103

12.0 Interrupts....................................................................................................................... 104

13.0 Error Handling................................................................................................................111

14.0 Related Application Notes............................................................................................. 113

15.0 Revision History ............................................................................................................114

CAN Flexible Data-Rate (FD) Protocol Module

dsPIC33/PIC24 Family Reference Manual

DS70005340A-page 2 2018 Microchip Technology Inc.

1.0 INTRODUCTION

CAN Flexible Data-Rate (FD) addresses the increasing demand for bandwidth on CAN buses.

The two major enhancements over CAN 2.0B consist of:

• Increased data field up to 64 data bytes (currently 8 bytes)

• Option to switch to faster bit rate after the arbitration field

Figure 1-1 shows the possible increase in net bit rate due to the higher Data Bit Rate (DBR) and

increased data bytes per frame (© Robert Bosch GmbH).

Figure 1-1: Net CAN FD Bit Rate

The CAN FD protocol is defined to allow CAN 2.0 messages and CAN FD messages to co-exist

on the same bus. This does not imply that non-CAN FD controllers can be mixed with CAN FD

controllers on the same bus. Non-CAN FD controllers will generate error frames while receiving

a CAN FD message.

1.1 Features

The CAN FD module has the following features:

General

• Nominal (Arbitration) Bit Rate up to 1 Mbps

• Data Bit Rate up to 8 Mbps

• CAN FD Controller modes:

- Mixed CAN 2.0B and CAN FD mode

- CAN 2.0B mode

• Conforms to ISO11898-1:2015

Message FIFOs

• 31 FIFOs Configurable as Transmit or Receive FIFOs

• One Transmit Queue (TXQ)

• Transmit Event FIFO (TEF) with 32-Bit Timestamp

Message Transmission

• Message Transmission Prioritization:

- Based on priority bit field and/or

- Message with lowest ID gets transmitted first using the TXQ

• Programmable Automatic Retransmission Attempts: Unlimited, 3 Attempts or Disabled

Frame ID: 11-Bit, Bit Rate Arbitration: 1 Mbit

2018 Microchip Technology Inc. DS70005340A-page 3

CAN FD Protocol Module

Message Reception

• 32 Flexible Filter and Mask Objects

• Each Object can be Configured to Filter either:

- Standard ID and first 18 data bits or

- Extended ID

• 32-Bit Timestamp

• The CAN FD Bit Stream Processor (BSP) implements the Medium Access Control of the

CAN FD protocol described in ISO11898-1:2015. It serializes and deserializes the bit

stream, encodes and decodes the CAN FD frames, manages the medium access,

Acknowledges frames, and detects and signals errors.

• The TX handler prioritizes the messages that are requested for transmission by the

transmit FIFOs. It uses the RAM interface to fetch the transmit data from RAM and provides

it to the BSP for transmission.

• The BSP provides received messages to the RX handler. The RX handler uses an

acceptance filter to filter the messages that shall be stored in the receive FIFOs. It uses the

RAM interface to store received data into RAM.

• Each FIFO can be configured either as a transmit or receive FIFO. The FIFO control keeps

track of the FIFO head and tail, and calculates the user address. In a TX FIFO, the user

address points to the address in RAM where the data for the next transmit message is

stored. In an RX FIFO, the user address points to the address in RAM where the data of the

next receive message will be read. The user notifies the FIFO that a message is written to

or read from RAM by incrementing the head/tail of the FIFO.

• The TXQ is a special transmit FIFO that transmits the messages based on the ID of the

messages stored in the queue.

• The TEF stores the message IDs of the transmitted messages.

• A free-running Time Base Counter (TBC) is used to timestamp received messages.

Messages in the TEF can also be timestamped.

• The CAN FD controller module generates interrupts when new messages are received or

when messages are transmitted successfully.

dsPIC33/PIC24 Family Reference Manual

DS70005340A-page 4 2018 Microchip Technology Inc.

Figure 1-2 shows the System Block Diagram.

Figure 1-2: System Block Diagram

TX Handler

TX Prioritization

RX Handler

Filter and Masks

Timestamping

Interrupt Control

Error Handling Diagnostics

CxTX

CxRX

Device RAM

TEF

Message

Object 0

Message

Object 31

•

TXQ

Message

Object 0

Message

Object 31

•

FIFO 1

Message

Object 0

Message

Object 31

•

FIFO 31

Message

Object 0

Message

Object 31

•

•••

2018 Microchip Technology Inc. DS70005340A-page 5

CAN FD Protocol Module

2.0 CAN FD MESSAGE FRAMES

The ISO11898-1:2015 describes the different CAN message frames in detail. Figure 2-1

through Figure 2-6 explain and summarize the construction of the messages and fields.

There are four different CAN data/remote frames (see Figure 2-2):

•CAN Base Frame: Classic CAN 2.0 frame using Standard ID

•CAN FD Base Frame: CAN FD frame using Standard ID

•CAN Extended Frame: Classic CAN 2.0 frame using Extended ID

•CAN FD Extended Frame: CAN FD frame using Extended ID

There are no remote frames in CAN FD frames; therefore, the RTR bit is replaced with the RRS

bit (see Figure 2-2). The RRS bit in the CAN FD base frame can be used to extend the SID to

12 bits. When enabled, it is referred to as SID11, it is the LSB of SID<11:0>.

Figure 2-3 specifies the control field of the different CAN messages. Before CAN FD was added

to the ISO11898-1:2015, the FDF bit was a reserved bit. Now the FDF bit selects between

Classic and CAN FD formats.

The BRS bit selects if the bit rate should be switched in the data phase of CAN FD frames.

Figure 2-6 illustrates the error and overload frames. These special frames do not change.

2.1 ISO vs. NON-ISO CRC

To support the system validation of non-ISO CRC ECUs, the CAN FD controller module sup-

ports both ISO CRC (according to ISO11898-1:2015) and non-ISO CRC (see Figure 2-4 and

Figure 2-5). The CRC field is selectable using the ISOCRCEN bit (C1CONL<5>). The ISO CRC

field contains the stuff count. This count was not included in the original CAN FD specification; It

was added to fix a minor issue in the error detection of the original specification.

CAN FD frames use two different lengths of CRC: 17-bit for up to 16 data bytes and 21-bit for

20 or more data bytes. Technically, there are a total of six different CAN data/remove frames in

the CAN FD.

Figure 2-1: General Data Frame

Note: If an error is detected during the data phase of a CAN FD frame, the bit rate will be

switched back to the Nominal Bit Rate (NBR). Error frames are always transmitted

at the arbitration bit rate.

IFS

(= 3b)

SOF

(1b) ARBITRATION (12/32b) CTRL (6/8/9b) DATA

(0 to 64b)

CRC (16/18/22b)

CRC (16/22/26b) ACK (2b) EOF (7b) IFS

(= 3b)

DATA FRAME

dsPIC33/PIC24 Family Reference Manual

DS70005340A-page 6 2018 Microchip Technology Inc.

Figure 2-2: Arbitration Field

Figure 2-3: Control Field

Figure 2-4: ISO CRC Field

ARBITRATION (12/32b)

SID<10:0> RTR

SID<10:0> RRS

SID11

EID<28:18> SRR IDE EID<17:0> RTR

EID<28:18> SRR IDE EID<17:0> RRS

CAN Base

CAN FD Base

CAN Ext.

CAN FD Ext.

CTRL (6/8/9b)

IDE FDF

IDE ESI

FDF DLC<3:0>

FDF ESI DLC<3:0>

CAN Base

CAN FD Base

CAN Ext.

CAN FD Ext.

DLC<3:0>

FDF BRS DLC<3:0>

res BRS

CRC (16/22/26b)

CRC (15b)

CAN Base

CAN FD Base

CAN Ext.

CAN FD Ext.

CRC

CRC (17/21b)

BRS

DEL

CRC

DEL

STUFF

CNT (4b)

CRC

DEL

STUFF

CNT (4b)

CRC

DEL

2018 Microchip Technology Inc. DS70005340A-page 7

CAN FD Protocol Module

Figure 2-5: NON-ISO CRC Field

Figure 2-6: Error and Overload Frame

CRC (16/18/22b)

CRC (15b)

CAN Base

CAN FD Base

CAN Ext.

CAN FD Ext.

CRC

CRC (17/21b)

DEL

CRC

DEL

CRC

DEL

CRC

DEL

ANYWHERE WITHIN DATA FRAME ERRFLAG (6b) ERRDEL (8b) IFS (= 3b) or OVL

EOF or ERRDEL or OVLDEL OVLFLAG (6b) OVLDEL (8b) IFS (= 3b) or OVL

ERROR

OVERLOAD

dsPIC33/PIC24 Family Reference Manual

DS70005340A-page 8 2018 Microchip Technology Inc.

2.1.1 DLC ENCODING

The Data Length Code (DLC) specifies the number of data bytes a message frame contains.

Table 2-1 illustrates the encoding.

Table 2-1: DLC Encoding

Frame DLC Number of Data Bytes

CAN 2.0 and CAN FD 0 0

CAN 2.0 9-15 8

CAN FD 9 12

10 16

11 20

12 24

13 32

14 48

15 64

2018 Microchip Technology Inc. DS70005340A-page 9

CAN FD Protocol Module

3.0 CONTROL REGISTERS

CAN FD operations are controlled using the following Special Function Registers (SFRs). The

following registers are described later in this section:

•Register 3-1: C1CONH

•Register 3-2: C1CONL

•Register 3-3: C1NBTCFGH

•Register 3-4: C1NBTCFGL

•Register 3-5: C1DBTCFGH

•Register 3-6: C1DBTCFGL

•Register 3-7: C1TDCH

•Register 3-8: C1TDCL

•Register 3-9: C1TBCH

•Register 3-10: C1TBCL

•Register 3-11: C1TSCONH

•Register 3-12: C1TSCONL

•Register 3-13: C1VECH

•Register 3-14: C1VECL

•Register 3-15: C1INTH

•Register 3-16: C1INTL

•Register 3-17: C1RXIFH

•Register 3-18: C1RXIFL

•Register 3-19: C1RXOVIFH

•Register 3-20: C1RXOVIFL

•Register 3-21: C1TXIFH

•Register 3-22: C1TXIFL

•Register 3-23: C1TXATIFH

•Register 3-24: C1TXATIFL

•Register 3-25: C1TXREQH

•Register 3-26: C1TXREQL

•Register 3-27: C1FIFOBAH

•Register 3-28: C1FIFOBAL

•Register 3-29: C1TXQCONH

•Register 3-30: C1TXQCONL

•Register 3-31: C1TXQSTA

•Register 3-32: C1FIFOCONxH

•Register 3-33: C1FIFOCONxL

•Register 3-34: C1FIFOSTAx

•Register 3-35: C1TEFCONH

•Register 3-36: C1TEFCONL

•Register 3-37: C1TEFSTA

•Register 3-38: C1FOUAxH

•Register 3-39: C1FOUAxL

•Register 3-40: C1TEFUAH

•Register 3-41: C1TEFUAL

•Register 3-42: C1TXQUAH

•Register 3-43: C1TXQUAL

•Register 3-44: C1TRECH

•Register 3-45: C1TRECL

•Register 3-46: C1BDIAG0H

•Register 3-47: C1BDIAG0L

•Register 3-48: C1BDIAG1H

•Register 3-49: C1BDIAG1L

•Register 3-50: C1FLTCONxH

•Register 3-51: C1FLTCONxL

•Register 3-52: C1FLTOBJxH

•Register 3-53: C1FLTOBJxL

•Register 3-54: C1MASKxH

•Register 3-55: C1MASKxL

dsPIC33/PIC24 Family Reference Manual

DS70005340A-page 10 2018 Microchip Technology Inc.

R/W-0 R/W-0 R/W-0 R/W-0 S/HC-0 R/W-1 R/W-0 R/W-0

TXBWS3 TXBWS2 TXBWS1 TXBWS0 ABAT REQOP2 REQOP1 REQOP0

bit 15 bit 8

R-1 R-0 R-0 R/W-1 R/W-1 R/W-0 R/W-0 R/W-0

OPMOD2 OPMOD1 OPMOD1 TXQEN

(1)

STEF

(1)

SERRLOM

(1)

ESIGM

(1)

RTXAT

(1)

bit 7 bit 0

Legend: S = Settable bit HC = Hardware Clearable bit

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-12 TXBWS<3:0>: Transmit Bandwidth Sharing bits

1111-1100 = 4096

1011 = 2048

1010 = 1024

1001 = 512

1000 = 256

0111 = 128

0110 = 64

0101 = 32

0100 = 16

0011 = 8

0010 = 4

0001 = 2

0000 = No delay

bit 11 ABAT: Abort All Pending Transmissions bit

1= Signals all transmit buffers to abort transmission

0= Module will clear this bit when all transmissions are aborted

bit 10-8 REQOP<2:0>: Request Operation Mode bits

111 = Sets Restricted Operation mode

110 = Sets Normal CAN 2.0 mode; error frames on CAN FD frames

101 = Sets External Loopback mode

100 = Sets Configuration mode

011 = Sets Listen Only mode

010 = Sets Internal Loopback mode

001 = Sets Disable mode

000 = Sets Normal CAN FD mode; supports mixing of full CAN FD and Classic CAN 2.0 frames

bit 7-5 OPMOD<2:0>: Operation Mode Status bits

111 = Module is in Restricted Operation mode

110 = Module is in Normal CAN 2.0 mode; error frames on CAN FD frames

101 = Module is in External Loopback mode

100 = Module is in Configuration mode

011 = Module is in Listen Only mode

010 = Module is in Internal Loopback mode

001 = Module is in Disable mode

000 = Module is in Normal CAN FD mode; supports mixing of full CAN FD and Classic CAN 2.0 frames

bit 4 TXQEN: Enable Transmit Queue bit

(1)

1= Enables TXQ and reserves space in RAM

0= Does not reserve space in RAM for TXQ

Note 1: These bits can only be modified in Configuration mode (OPMOD<2:0> =

100

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