Course Introduction

Purpose

• This training course provides an overview of the CAN peripheral in Renesas M16C and R8C microcontrollers that is used to build networked, multiprocessor embedded systems, and the Application Programming Interface (API) used to program that on-chip CAN peripheral.

Objectives

• Get an introduction to the Renesas M16C and R8C CAN peripheral hardware.

• Understand how to program the CAN peripheral using the Renesas API function calls.

Content

• 29 pages

• 4 questions

Learning Time

• 45 minutes

MCU data bus

MCU data bus

CAN bus timing control register

CAN control register

Message control registers 0 to 15

CAN global mask register

CAN local mask register A

CAN local mask register B

Acceptance filter slots 0 to 15

16-bit timer

Timestamp register(not in R8C/23)

Message boxes (Slots 0 to 15)

• Message ID • DLC• Data field• Timestamp

CAN status register

CAN slotstatus register

CAN interruptcontrol register

CAN receive errorcount register

CAN transmit errorcount register

CTx

CRx

CAN receive complete

CAN transmit complete

CAN error

CAN wakeup

CAN extended ID register

Interruptcontrol logic

To/From External CAN Transceiver

Protocol controller

Wakeuplogic

M16C/R8C MCU CAN Peripheral

Message Boxes

006016

006116

006216

006316

006416

006516

006616

006716

006816

006916

006A16

006B16

006C16

006D16

006E16

006F16

Message ID(Standard, Extended)

DLC(6 Bytes)

Data Field(8 Bytes)

Timestamp Value(2 Bytes)

Communication performed via CAN message boxes:

• Message boxes– Transmit and receive buffers for CAN

messages– Comprise 16 slots of 16 bytes

(or 8 words) each – Slots 14 and 15 can be used for

BasicCAN slots

• Individual slots can be set as transmit or receive slots by a program

• During both transmit and receive operation, slots with the lowest numbers have highest priority; i.e., priority increases as slot number decreases

• Each slot retains its previous contents until a new message is sent or received

.

Interrupt sources:• CAN receive complete• CAN transmit complete• CAN error (error passive state, bus off state, bus error)• CAN wakeup

Related registers:• Interrupt control registers (C0RECIC, C0TRMIC, C01ERRIC, [C01WKIC])

– Set priority levels for interrupt sources listed above• CAN interrupt control register (C0IRC)

– Enables and disables interrupts for individual message box slots

Interrupt Control Logic

#pragma INTERRUPT /B fnc_c0recic(); #pragma INTERRUPT /B fnc_c0trmic();

An interrupt service function must be declared with ‘pragma’ somewhere in the program.

Examples:

Renesas M16C CAN peripheral API

set_mask_can ( )

config_can ( )

set_rec_std_dataframe_can ( slot_nr, id )check_rec_success_can ( slot_nr, dataframe* ) – if polling

get_message_can ( slot_nr, dataframe* )

set_bitrate_can ( )

abort_trm_can ( slot_nr )check_err_can ( )

fnc_c0recic ( ) – if using interrupts

can_initial ( )

fnc_c0trmic ( ) – if using interrupts

set_trm_std_dataframe_can ( slot_nr, dataframe* )check_trm_std_dataframe_can ( slot_nr) – if polling

check_hw_tmr_can ( canblock1_tmo_diag* )

Error functions

Initialization functions

Transmit functions

Receive functions

config_can ( )

• Transition to CAN reset/ initialization mode

• Enable CAN ports

• Set operating mode

• Set bit timing and baud rate

• Set mask registers

• Transition to CAN operating mode

Initializing CAN PeripheralCAN Configuration Procedure

START

Enter CAN reset/ initialization mode

Exit CAN sleep mode

CAN reset mode?NO

YES

Enable CAN ports

Set CAN control register - Loopback mode select bit - Message order select bit - Basic CAN mode select bit - Bus error interrupt enable bit - Timestamp prescaler

Set CAN bit timing and baud rate

Set mask register

Go to CAN operation mode

CAN operation mode?NO

END

YES

START

END

Set interruptpriority level

Clear interruptenable flag

Set interruptenable flag

Enable CAN interrupts

If using CAN interrupts

Set Baud Rate and Bit Timing

END

Set CAN clockdivide-by-N value

Clear protect register

Set:• Prescaler divide-by-N value• Sampling count• PTS, PBS1, PBS2, SJW

Setting CAN bit timing and baud rate

START

Set protect register

• Cancel register protect

• Set divide ratio for CAN clock

• Set register protect

• Set dividing ratio for prescaler

• Set sampling count

• Set sampling points PTS, PBS1, PBS2, and SJW

set_bitrate_can ( )

Is the following statement true or false? Click Done when you are finished.

“The R8C/M16C CAN peripheral provides 16 message boxes, each of which has transmit and receive buffers. The message buffers comprise 16 slots of 16 bytes (or 8 words).”

True

False

Done

Question

Sets up a slot to transmit:1. Check if transmit possible [ “TrmActive” = 0?]2. Clear message control register3. Prohibit interrupts for slot (if using TX interrupts)4. Select standard or extended ID5. Set TX-ID6. Byte count of transmit data (set DLC)7. Set transmit data 8. Interrupt enable the slot (if using TX interrupts)9. Transmit data frame

Data Frame Transmit Mode

set_trm_std_dataframe_can ( slot_nr, dataframe* )

If multiple slots are set to data frame transmit mode simultaneously,

they transmit in order, starting with slot with lowest number

Keep interrupt code short to avoid blocking other interrupts.

Confirming Successful Transmission using

an Interrupt

CAN successful transmission interrupt

routine START

Check that slot finished sending

Notify application etc.

CAN successful transmission interrupt

routine END

Performs successful data frame transmit interrupt routine:

• Sets a flag so main program knows what data was successfully sent out

• Notify application• Flash an LED, etc.

fnc_c0trmic ( )

Verify Successful Transmission

Transmitting the highest-priority message

Message transmission Error frame Message retransmission ReceptionReceiving

Error Arbitration loss

Transmit abort request

Transmit request

Time limit

Applying a time limit to message transmission

Message (1) transmission Reception Message (2) transmission

Arbitration loss

Transmit abort request Transmission request for now highest priority message (2)

Transmit Abort

Transmit Abort

Abort transmissionprocedure

START

Transmitrequested?

Request abort transmission

END

NO

YES

Beingtransmitted?

NO

YES

Send priority message

Ab

ort

tra

nsm

issi

on

re

qu

est

s u

nn

ece

ssa

ry

abort_trm_can ( in_slot )

• Transmit incomplete? “SentData” = 0?

• Transmit abort request “TrmReq” 0

• When transmit abort complete, transmit highest-priority message

Data Frame Receive

set_rec_std_dataframe_can ( slot_nr, id )

Functions performed:

• Set up slot for receive

• Prohibit interrupts for slot (if using RX interrupts)

• Set Standard or Extended ID

• Set RX-ID

• Clear message control register

• Set data frame receive mode

• Set RecReq to 1 to start receiving

• Enable interrupts for the receive slot (if using RX interrupts)

Question

a. set_rec_std_dataframe_can

b.abort_trm_can

c. set_trm_std_dataframe_can

d.set_bitrate_can

Which of the following functions is used to set up a slot to receive? Select the response that applies and click Done.

Done

Example 2: Receiving standard data frames/remote frames with IDs 122 and 123 in CAN slot 0

Slot 0 sees on busMask register

Received message

C0GMRID123

1 1 1 1 1 0 0 1 0 0

0 0 1 0 0 1 1 1 1 1 01 0 0 0 1 X

1 0 0 0 1 1

SID10-6 SID5-0

ID122 0 0 1 0 0 1 0 0 0 1 0

This function does the following:• Accept one ID for message box => sets MASK to all ones• Accept all messages => sets MASK to all zeros• Accept range of messages => sets the ‘don’t-care’ bits of ID to

zero in MASK

Mask Setting

Example 1: Receiving standard data frame/ remote frame with ID 123 in CAN slot 0

Slot 0 sees on busMask registerReceived message

C0GMRID123

1 1 1 1 1 0 0 1 0 0

0 0 1 0 0 1 1 1 1 1 11 0 0 0 1 1

1 0 0 0 1 1

SID10-6 SID5-0

set_mask_can ( )

Acceptance Filter Support Unit

The ASU function:• Determines if received Standard IDs are valid• Provides faster response than software filtering

Acceptance filtersupport registers Received ID (11 bits)

Upper 8 bits of received ID

Converted value of lower3 bits of received ID

Register configuration during read operation

CSID7 CSID6 CSID5 CSID4 CSID3 CSID2 CSID1 CSID0 SID10 SID9 SID8 SID7 SID6 SID5 SID4 SID3

Converted value of lower 3 bits of received ID Upper 8 bits of received ID

b0b15 b8 b7

(ASU registers: C0AFS, C1AFS)

Receive Complete using Polling

Confirming by Polling

START

Finished receivingsuccessfully?

Process received message

END

NO

YES

Data received?

If yes: process received message

Note: Check for overruns!

CAN slot status register or “NewData” in CAN message control register

• Copy data to buffer

• Notify main program that data was received

Receive Complete using Interrupt

CAN successful reception interrupt

routine START

END

Processing for received message

Check that the slot finished receiving

successfully

Confirming successful reception with a CAN successful reception interrupt fnc_c0recic ( )

• Checks whether or not received data to slot is complete

• Looks at receive complete flag (NewData)

• Reads received message

• Checks for more received data before leaving (to reduce ‘nr’ of interrupts)

Dataframe = pointer to a dataframe structure

Received Message Processing

check_rec_success_can ( slot_nr, dataframe )

get_message_can ( slot_nr, dataframe )

Match each CAN API function to the most appropriate explanation by dragging the letters on the left to the correct locations on the right. Click Done when you are finished.

set_trm_std_dataframe_can

fnc_c0recicB C

Done ResetShow

Solution

ATells main application that message has been sent successfullyD

C ASU

Determines if received Standard IDs are valid

BExecuted when an interrupt verifies successful data frame reception

D fnc_c0trmic A Sets up a slot to transmit

Question

Prescaler (Divide by 1, 2, 4, or 8)

16-bit free-running counter

Received ID

Received data

Timestamp

Receive slot

Standard cycle: 1-bit-time cycle

Reset by software

Cycle and initializationare programmable

Timestamp Function

This function:• Automatically writes

timestamp during normal receive operation

• Useful for determining sequence in which a group of messages was received

Polled message boxes - check which slots have new data

Receive interrupts - check Active Slot Bits for which slot has received last

(If the CAN receive interrupts are used)

1. Set interrupt priority level2. Clear interrupt request bit

3. Set slot ICR enable flag 4. Set receive enable bit (I flag) Flag registers

At system setup time:

Running:

What Slots Have New Data?

CAN receive interruptcontrol register (c0recic)

“NewData” in CAN message control register

CAN status registerReceived message processing

CAN error generated?CAN bus error handling:

• CAN error passive state?– Error passive handling

• CAN bus off state?– Bus off handling

Error Confirmation (Interrupt Processing)

CAN bus off state?• CAN return from bus off

Error Confirmation (Polling Processing)

Error Handling

check_err_can ( )

CAN status register

CAN Status

Register

b15 b14 b13 b12 b11 b10 b2 b1 b0

CAN Status Register

Error bus off state flag

Error passive state flag

ErrorActiveState-Normal

Bus error state flagSet if any

Error frame

ErrorPassive

State

BusOff

State- too many errorsstop transmitting

Error!

Error!

Error!

Data Frames

ErrorPassive

State- more than 128 erros

Return From Bus Off State

BusOff

State

ErrorActiveState

Slot’s state changes when

- Slot receives 11 consecutive recessive bits 128 times

- ‘Return from bus off’ function is executed

CAN control register

Sets return from bus off bit to 1

1

b11

‘Return from bus off’ function

CAUTION

- A node is supposed to go bus off if it is faulty. Use this function with care so a faulty node doesn’t keep coming back.

Loopback Function

This function does the following:• Allows confirmation of transmitted content

– Useful as self-diagnostic during debugging, etc.

Transmit slot

Receive slot

Message transmission

Transmit Unit

Same ID set for transmitand receive slot C

AN

BusOL

O

PB

AC

K

Listen-Only Mode

• Normal receive completed: ACK output• Communication error: Error frame output

No ACK or error frame transmit operations are performed

Transmit unit

GettingResponses

Receive unit(Listen-Only

mode)

Receive unit

Receive unit

Receive unitNormal mode

TransmittingMessage

Transmit unit

Receive unit

Receive unit(Listen-Only

mode)

For more CAN API information:

• CAN Application Note — Data on API for R8C and M16C MCUs; download fromhttp://documentation.renesas.com/eng/products/mpumcu/apn/rej05b0276_16ccanap.pdf

• CAN Specification Version 2.0, 1991, Robert Bosch GmbH

• M16C/6NK, M16C/1N, M16C/29, R8C/23, etc. hardware manuals

Question

Which of these statements correctly describe error handling, slot status and other issues? Select all that apply and then click Done.

The polling approach to error confirmation uses the bus error state flag, error active status flag, and bus off status flag in the CAN status register.

A slot returns from the bus off state when it receives 11 consecutive recessive bits 128 times or when a ‘Return from bus off’ function executes.

The loopback function is useful as self-diagnostic during debugging because it can confirm transmitted content.

A receive unit in listen-only mode doesn't transmit ACKs or error frames.

Done

• CAN peripheral in R8C and M16C microcontrollers

• Initializing the CAN peripheral

• CAN API functions

Course Summary