NXP Semiconductors LPC5500 Series Manual de usuario

1 Introduction

The LPC55S1x/LPC55S0x features a CAN controller supporting CAN-FD.

LPC5500 series SDK provides the mcan_interrupt_transfer example

demonstrates the use of CAN to transfer data. Based on this example,

this application note describes how to use CAN-FD’s Bit Rate Switch and

transmitter delay compensation features. Enabling these two features can

improve throughput and eliminate the bit error caused by transmitter delay.

2 CAN-FD

CAN-FD is defined in the international standard ISO 11898-1:2015. For quick

start on using CAN-FD, this section introduces some key features of CAN-FD

and aims the users who are familiar with CAN.

2.1 Differences between CAN and CAN-FD

There are two key differences between classical CAN and CAN-FD. The first is that CAN-FD can use much higher bitrates than

classical CAN. Classical CAN is limited to 1 Mbit/s. CAN-FD does not have a theoretical limit, but in practice it is limited by the

transceivers. The second key difference is the increased amount of data per CAN message. Classical CAN is limited to 8 bytes.

CAN-FD limit is increased eight-fold to 64 bytes per message.

With the increased amount of data per CAN message, CAN-FD frames need higher bit rate to decrease the delay time in the

communication and increase real-time performance. The CAN-FD frames can reach higher bit rates through enabling bitrate

switch feature.

On the other hand, the bit rate is higher, the bit time is shorter. In order to enable a data phase bit time that is even shorter than the

transmitter delay, the delay compensation is introduced. Without transmitter delay compensation, the bit rate in the data phase

of a CAN-FD frame is limited by the transmitter delay.

2.2 Bit Rate Switch

In the CAN-FD frame control phase, data phase, and CRC phase are transmitted with a higher bit rate than the beginning and the

end of the frame.

The Bit Rate Switch feature is enabled by setting the BRSE bit in the CCCR register. When enabling the Bit Rate Switch, we also

need to set arbitration phase bit rate (before enabling Bit Rate Switch) and data phase bit rate (after enabling Bit Rate Switch)

correctly. The arbitration phase bit rate is set by the NBTP register, the data phase bit rate is set by DBTP register.

2.3 Transmitter delay compensation

The protocol unit of the MCAN has implemented a delay compensation mechanism to compensate the transmitter delay. The

transmitter delay compensation enables configurations where the data bit time is shorter than the transmitter delay, that is

described in detail in the new ISO11898-1. It is enabled by setting the TDC bit in the DBTP register. The TDCO field in the TDCR

register is used for setting the transmitter delay compensation offset. The offset value defines the distance between the measured

delay from m_can_tx to m_can_rx and the secondary sample point. The transmitter delay compensation offset and secondary

sample point are show in Figure 1.

Contents

1 Introduction......................................1

2 CAN-FD...........................................1

2.1 Differences between CAN and

CAN-FD....................................... 1

2.2 Bit Rate Switch.............................1

2.3 Transmitter delay compensation

.....................................................1

3 Demonstration.................................2

3.1 Hardware environment.................2

3.2 Software environment..................3

3.3 Using CAN-FD steps overview.... 3

3.4 Config CAN-FD Bit Rate Switch...4

3.5 Steps and results......................... 5

4 Revision history...............................6

AN12728

How to Use CAN-FD to Transfer Data on LPC5500 Series

Rev. 3 — 17 June, 2021 Application Note

Figure 1. MCAN transmitter delay compensation offset and secondary sample point

3 Demonstration

This section provides a brief introduction of how to use CAN-FD to transfer data and enable the Bit Rate Switch and transmitter

delay compensation. It is based on the LPC5500 series SDKs mcan_interrupt_transfer example.

3.1 Hardware environment

•Boards

— Two LPCXpresso55S16/LPCXpresso55S08 boards

•Miscellaneous

— Two Micro USB cables

— One 120 Ω terminated CAN cable

— Personal Computer

•Board setup

CAN shields are connected to evaluation boards. Connect the micro USB cable between PC and J19 on the evaluation board

for loading and running a demo. This is also used for UART communication to UART terminal on the PC. Taking LPC55S16 as

example, Figure 2 shows the board setup and CAN connections.

NXP Semiconductors

Demonstration

How to Use CAN-FD to Transfer Data on LPC5500 Series, Rev. 3, 17 June, 2021

Application Note 2 / 7

Figure 2. Boards setup and CAN connection

3.2 Software environment

•Tool chain

— Keil or MCUXpresso11.1 or above

•Software package

— LPC55S16/LPC55S08 SDK (V2.9.0)

•UART terminal program

— PuTTY, or similar one

3.3 Using CAN-FD steps overview

The LPC5500 series SDK driver example: mcan demonstrates how to use CAN-FD to transfer data. In this example, the following

steps are required:

• Set the system clock

• Set the MCAN clock

— Divide the system clock for MCAN module

• Initialize MCAN

— Enable the MCAN clock

— Reset the MCAN module

NXP Semiconductors

Demonstration

How to Use CAN-FD to Transfer Data on LPC5500 Series, Rev. 3, 17 June, 2021

Application Note 3 / 7

— Configure the MCAN Control Register, enable the CAN-FD and Bit Rate Switch

— Set arbitration phase bit rate and data phase bit rate

— Enable transmitter delay compensation

• Set Message RAM

• Set message ID filter configuration and element

• Set the configuration of Rx FIFO and Tx buffer

• Enter MCAN normal mode

• Transfer data

— Configure Tx frame data and send

— Receive data

On the LPC5500 series SDKs mcan_interrupt_transfer example, it uses the classical CAN nodes on bus by default. The needs

of data phase bit rate setting are same as the arbitration phase bit rate setting. They should comply classical CAN-bus protocol.

But in the example of this document, it uses the CAN-FD nodes on the bus. The CAN-FD arbitration phase bit rate is set to 1 Mbit/s

and the data phase bit rate is set to 5 Mbit/s. It needs to enable Bit Rate Switch and transmitter delay compensation features.

The following sections introduce some key steps for using CAN-FD.

3.4 Config CAN-FD Bit Rate Switch

Enabling the CAN-FD Bit Rate Switch can increase the throughput. In this example, it calls the MCAN_SetBaudRate() function to

set arbitration phase bit rate and calls the MCAN_SetBaudRateFD() function to set data phase bit rate. The MCAN clock had be

set to 60 MHz.

3.4.1 Set arbitration phase bit rate to 1 Mbps

As per the CAN specification definition, the Nominal Bit Rate is the number of bits per second transmitted in the absence of

resynchronization by an ideal transmitter. The Nominal Bit Rate and the Nominal Bit Time relationship is NOMINAL BIT TIME =

1 / NOMINAL BIT RATE. So, if the arbitration phase bit rate is set to 1 Mbit/s, the arbitration phase bit time is 1 µs.

The time quantum (t_q) is a fixed unit of time derived from the MCAN clock period. There exists a programmable prescaler, with

integral values, ranging at least from 1 to 32. Starting with the MCAN clock period, the t_q can have a length of

t_q = m * MCAN clock period = m / MCAN clock

with m the value of the prescaler.

In the MCAN_SetBaudRate() function, we need to define a variable, whose type is mcan_timing_config_t, for setting the arbitration

phase bit time. The structure mcan_timing_config_t is defined in Figure 3.

Figure 3. MCAN protocol timing characteristic configuration structure

The prescaler m is equivalent to (preDivider + 1). The t_q can have a length of

t_q = (preDivider + 1) / 60 MHz = (preDivider + 1) / 60 (µs)

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Demonstration

How to Use CAN-FD to Transfer Data on LPC5500 Series, Rev. 3, 17 June, 2021

Application Note 4 / 7

with the structure element preDivider.

The total number of t_q in an arbitration phase bit time may be programmed in the range of 4 to 385 time quanta. The length of

Arbitration phase bit time = MCAN_TIME_QUANTA_NUM_ARBIT * t_q

. We define a macro MCAN_TIME_QUANTA_NUM_ARBIT as 20 in this example. The arbitration phase bit time is 1 µs, t_q is 1/20

µs, preDivider is 2.

The macro

MCAN_TIME_QUANTA_NUM_ARBIT = 1 + (seg1 + 1) + (seg2 + 1)

The structure elements seg1 and seg2 stands for phase buffer segment 1 and 2 minus one respectively. We set the element seg1

to the value 13, and the element seg2 to 4 in this example. Calling the updated function MCAN_SetBaudRate(), we finish setting

the arbitration phase bit rate to 1 Mbit/s.

3.4.2 Set data phase bit rate to 5 Mbps

Setting the data phase bit rate is similar to setting the arbitration phase bit rate. The data phase bit rate is set in the

MCAN_SetBaudRateFD() function.

The one of differences is that the total number of t_q in a data phase bit time may be programmed in the range of 4 to 49

time quanta.

In this example, we define a macro MCAN_TIME_QUANTA_NUM_DATA as 12 as the total number of t_q in a data phase

bit time. The element seg1 is 7, the element seg2 is 2 and the element preDivider is 4. Calling the updated function

MCAN_SetBaudRateFD(), we finish setting the data phase bit rate to 5 Mbit/s which is the highest bit rate that the onboard

transceiver can support.

3.4.3 Enable Bit Rate Switch

Setting the MCAN CCCR register’s BRSE bit to 1 enables the Bit Rate Switch for CAN-FD. In the example of this application note,

the control phase, data phase, and CRC phase of CAN_FD frame are transmitted at the bit rate of 5 Mbit/s, while the other phases

of a CAN-FD frame are transmitted at the bit rate of 1 Mbit/s.

3.5 Steps and results

On this CAN-FD demo, there are two nodes on the bus to transmit and receive data. One node is selected as A, and another

node is selected as B. Press any key on the node A's terminal console to trigger one-shot transmission. The node B receives this

one-shot transmission data and sends it back to node A. Node A receives the data and this one-shot transmission finishes.

The basic steps are:

1. Hardware setup

See section 3.1 for boards setup and CAN connection.

2. Build and download

• Import the software package of this demo to the MCUXpresso IDE and build.

• Download the executable file using debugger.

3. Setup for UART terminal programs

• Check the COM number which is simulated as LPC-LinkII in Device Manager on PC.

• Open two UART terminal programs on PC and connect one evaluation board with one UART terminal program.

Configure the communication protocol as 115200 + 8 + N + 1.

4. Run

Reset two evaluation boards by pressing the SW1(reset) button on each board. One evaluation board selects as node A,

another selects as node B. Press any key on the node A terminal console to trigger one-shot transmission. The message

displays on the node A terminal is shown in Figure 4 and the message displays on the node B terminal is shown in Figure 5 .

NXP Semiconductors

Demonstration

How to Use CAN-FD to Transfer Data on LPC5500 Series, Rev. 3, 17 June, 2021

Application Note 5 / 7

Figure 4. Messages printed on the node A terminal

Figure 5. Messages printed on the node B terminal

4 Revision history

Revision number Date Substantive changes

0 02/2020 Initial release

1 03/2020 Updated Software environment due to MCUXpresso tool version

change

2 10/2020 Replaced LPC55S16 with LPC5500 series

3 17 June, 2021 • Updated Software environment due to MCUXpresso tool

version change

• Removed Config Transmitter Delay Compensation

NXP Semiconductors

Revision history

How to Use CAN-FD to Transfer Data on LPC5500 Series, Rev. 3, 17 June, 2021

Application Note 6 / 7

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Date of release: 17 June, 2021

Document identifier: AN12728

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