WS-TTL-CAN Mini Module Can Conversion Protocol

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Product Specifications

• Model: WS-TTL-CAN
• Supports bidirectional transmission between TTL and CAN
• CAN parameters (baud rate) and UART parameters are configurable
  via software

Product Usage Instructions

1. Quick Start

To quickly test transparent transmission:

1. Connect the WS-TTL-CAN device
2. Follow the instructions in the user manual for transparent
   transmission test

2. Function Introduction

• Hardware Features: Describe hardware features
  here.

• Device Features: Explain device features in
  detail.

3. Module Hardware Interface

• Module Dimensions: Provide module
  dimensions.

• Module Pin Definition: Detail the pin
  definitions for proper connection.

4. Module Parameter Setting

Configure module settings using the provided Serial Server
Configure Software.

5. UART Parameter Setting

Adjust UART parameters as needed for your setup.

6. CAN Parameter Setting

Set CAN parameters, including baud rate, for proper
communication.

Frequently Asked Questions (FAQ)

Q: Can I upgrade the device firmware using the TTL

connection?

A: Yes, the device supports firmware upgrades via TTL for
convenient updates.

Q: How do I convert serial frames to CAN frames?

A: Refer to section 9.1.1 in the user manual for instructions on
serial frame to CAN conversion.

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WS-TTL-CAN
User Manual
WS-TTL-CAN User Manual
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WS-TTL-CAN
User Manual
Contents
1. OVERVIEW …………………………………………………………………………………………………………………….1 1.1 Features …………………………………………………………………………………………………………………1
2. QUICK START ………………………………………………………………………………………………………………. 2 2.1 Transparent Transmission Test …………………………………………………………………………… 2
3. FUNCTION INTRODUCTION ……………………………………………………………………………………….. 4 3.1 Hardware Features ………………………………………………………………………………………………..4 3.2 Device Features …………………………………………………………………………………………………….4
4. Module HARDWARE INTERFACE ……………………………………………………………………………….. 6 4.1 Module Dimensions ……………………………………………………………………………………………….6 4.1 Module Pin Definition …………………………………………………………………………………………… 7
5. MODULE PARAMETER SETTING ……………………………………………………………………………….. 8 5.1 Serial Server Configure Software …………………………………………………………………………8
6. CONVERSION PARAMETERS …………………………………………………………………………………… 10 6.1 Conversion Mode …………………………………………………………………………………………………10 6.2 Conversion Direction ………………………………………………………………………………………….. 11 6.3 CAN Identifier in UART ………………………………………………………………………………………. 11 6.4 Whether CAN is Transmitted in UART ………………………………………………………………. 12 6.5 Whether CAN Frame ID is Transmitted in UART ……………………………………………….12
7. UART PARAMETER SETTING …………………………………………………………………………………… 13 8. CAN PARAMETER SETTING ………………………………………………………………………………………14
8.1 CAN Baud Rate Setting ……………………………………………………………………………………… 14 8.2 CAN Filter Setting ………………………………………………………………………………………………. 15 9. CONVERSION EXAMPLE …………………………………………………………………………………………… 17 9.1 Transparent Conversion …………………………………………………………………………………….. 17
9.1.1 Serial Frame To CAN ……………………………………………………………………………………….17 9.1.2 CAN Frame To UART ……………………………………………………………………………………… 19

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9.2 Transparent Conversion with ID ………………………………………………………………………… 20 9.2.1 UART Frame To CAN ……………………………………………………………………………………… 20 9.2.2 CAN Frame To UART ……………………………………………………………………………………… 22
9.3 Format Conversion ………………………………………………………………………………………………23 9.4 Modbus Protocol Conversion ………………………………………………………………………………24

1. OVERVIEW

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WS-TTL-CAN is the device that supports the bidirectional transmission between TTL and CAN. The device’s CAN parameters (such as baud rate) and UART parameters are configurable via the software.

1.1 FEATURES
Support CAN to TTL bidirectional communication. Supports device firmware upgrade via TTL, more convenient for firmware update and function
customization Onboard interface with ESD isolated protection and anti-surge protection, and better EMC
performance. 14 sets of configurable filter 4 working modes: transparent conversion, transparent with identifiers conversion, format
conversion, and Modbus RTU protocol conversion With offline detection and self-restore function Compliant with CAN 2.0B standard, compatible with CAN 2.0A, and compliant with ISO
11898-1/2/3 CAN communication baudrate: 10kbps~1000kbps, configurable CAN buffer of up to 1000 frames ensures no data loss Supports high-speed conversion, the CAN transmission speed can reach up to 1270 extended
frames per second with the UART at 115200bps and CAN at 250kbps (close to the theoretical max value of 1309), and can exceed 5000 extended frames per second with the UART at 460800bps and CAN at 1000kbps

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2. QUICK START

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WS-TTL-CAN is the device that supports the bidirectional transmission between TTL and CAN. The device’s CAN parameters (such as baud rate) and UART parameters are configurable via the software.
The related software: WS-CAN-TOOL.

2.1 TRANSPARENT TRANSMISSION TEST

First, you can test it with the default parameters of the product, as shown below:

Item
TTL CAN Operation Mode
CAN Baud Rate CAN Sending Frame Type
CAN Sending Frame ID CAN Filter

Parameters
115200, 8, N, 1 Transparent Transmission, Bidirectional
250kbps Extended Frames
0 x 12345678 Disabled (Receive all CAN frames)

TTL and CAN transparent transmission test: Use the serial cable to connect the computer and the TTL port of the device, and connect the
USB to CAN debugger (the first time you use it, you need to install the software and driver, please consult the relevant manufacturers of the USB to CAN debugger for the detailed use), and then the 3.3V@40mA power adapter to power on the device.

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Figure 1.2.2: RS232 TO CAN Data Transparent Transmission
Open the SSCOM, select the COM port to be used, and set the UART parameters as shown in Figure 1.2.2. After setting, you can enter the serial port, open USB to CAN debugging software, and set the baud rate as 250kbps.
After following the above steps, the CAN and RS232 can send data to each other.
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3. FUNCTION INTRODUCTION

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WS-TTL-CAN has onboard 1-channel TTL interface and 1-channel CAN interface. The baud rate of the serial port supports 1200~460800bps; the baud rate of CAN supports 10kbps~1000kbps, and the firmware upgrade of the device can be realized through the TTL interface, which is very convenient to use.
Users can easily complete the interconnection of serial devices and CAN devices. 3.1 HARDWARE FEATURES

No.

Item

1

Model

2

Power

3

CPU

4

CAN Interface

5

TTL Interface

6 Communication Indicator

7

Reset/Restore Factory Setting

8

Operation Temperature

9

Storage Temperature

Parameters
WS-TTL-CAN 3.3V@40mA 32-bit High-performance Processor ESD Protection, Anti- surge Protection, Excellent EMC Performance The baud rate supports 1200~460800 RUN, COM, CAN indicator, easy to use Comes with the setting signal for Reset/ Restore Factory
Setting Industrial Grade: -40~85
-65~165

3.2 DEVICE FEATURES
Support the bidirectional data communication between CAN and TTL. The device parameters are configurable through TTL. ESD Protection, Anti-surge Protection, Excellent EMC Performance. 14 set configurable filters. Four operation modes: transparent conversion, transparent conversion with identifiers, format
conversion, and Modbus RTU protocol conversion. Offline detection and automatic recovery functionality. Compliance with CAN 2.0B specifications, compatible with CAN 2.0A; complies with ISO
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11898-1/2/3 standards. Baud rate range: 10kbps ~ 1000kbps. CAN buffer capacity of 1000 frames to prevent data loss. High-speed conversion: At a serial port baud rate of 115200 and CAN rate of 250kbps, the CAN
sending speed can reach up to 1270 extended frames per second (close to the theoretical maximum of 1309). At a serial port baud rate of 460800 and CAN rate of 1000kbps, the CAN sending speed can exceed 5000 extended frames per second.
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4. Module HARDWARE INTERFACE
4.1 MODULE DIMENSIONS

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4.1 MODULE PIN DEFINITION

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Label 1
2
3
4 5 6 7 8 9 10 11 12

Description UART_LED
CAN_LED
RUN_LED
NC CAN_H CAN_L 3.3V GND CFG DIR RXD TXD

Note TTL communication indicator signal pin, high level for no data, low level for
data transmission CAN communication indicator signal pin, high level for no data, low level for
data transmission System running indicator signal pin, toggles between high and low levels (approx. 1Hz) when system is working normally; Outputting high level when
CAN bus is abnormal Reserved pin, not connected CAN differential positive, built-in 120 resistor CAN differential negative, built-in 120 resistor
Power input, 3.3V@40mA Ground
Reset/restore to factory setting, pull low within 5s for resetting or more than 5s for restoring factory setting RS485 direction control TTL RX TTL TX

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5. MODULE PARAMETER SETTING

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This module can be configured by ” WS-CAN-TOOL” through the TTL interface. If you fail to connect the device due to your careless setting, you can press the “CFG” key to restore the factory setting, (Press and hold the CFG key for 5s, and release it after the three green indicators blink at the same time).
5.1 SERIAL SERVER CONFIGURE SOFTWARE

Select the connected “Serial Port”. Click on “Open Serial”. Click on “Read Device Parameters”.
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After reading the device parameters, you can modify them. You can click on “Save Device Parameters” to save your modification. Then you need to reboot the device.
The following content is for explaining the parameters in the configured software.
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6. CONVERSION PARAMETERS

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This section specifies the device’s conversion mode, conversion direction, the position of CAN identifiers in the serial sequence, whether CAN information is transformed to UART, and whether CAN frame IDs are transformed to UART.
6.1 CONVERSION MODE
Three conversion modes: transparent conversion, transparent conversion with identifiers, and format conversion.
Transparent conversion It involves converting bus data from one format to another without adding or modifying data. This
method facilitates an exchange of data formats without modifying the data content, making the converter transparent to both ends of the bus. It doesn’t add communication overhead for users and allows real-time, unaltered data conversion, capable of handling high-volume data transmission.
Transparent conversion with identifiers This is a special application of transparent conversion, also without adding a protocol. This
conversion method is based on the common characteristics of typical serial frames and CAN messages, allowing these two different types of buses to seamlessly form a single communication network. This method can map the “address” from the serial frame to the identifier field of the CAN message. The “address” in the serial frame can be configured in terms of its starting position and length, enabling the converter to adapt to user-defined protocols to the maximum extent in this mode.
Format conversion Additionally, the format conversion is the simplest usage mode, where the data format is defined
as 13 bytes, encompassing all information from the CAN frame.

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6.2 CONVERSION DIRECTION

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Three conversion directions: bidirectional, only UART to CAN, and only CAN to UART. Bidirectional
The converter converts data from the serial bus to the CAN bus and also from the CAN bus to the serial bus. Only UART to CAN
It only translates data from the serial bus to the CAN bus and doesn’t convert data from the CAN bus to the serial bus. This method effectively filters out interference on the CAN bus. Only CAN to UART
It exclusively translates data from the CAN bus to the serial bus and doesn’t convert data from the serial bus to the CAN bus.

6.3 CAN IDENTIFIER IN UART

This parameter only be effective when it is in “Transparent conversion with identifiers” mode:

When converting serial data to CAN messages, the offset address of the frame ID’s starting byte in the serial frame and the length of the frame ID are specified.
The frame ID length can range from 1 to 2 bytes for standard frames, corresponding to ID1 and
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ID2 in the CAN message. For extended frames, the ID length can range from 1 to 4 bytes, covering ID1, ID2, ID3, and ID4. In standard frames, the ID consists of 11 bits, while in extended frames, the ID consists of 29 bits. 6.4 WHETHER CAN IS TRANSMITTED IN UART
This parameter is only used in “Transparent Conversion” mode. When selected, the converter will include the frame information of the CAN message in the first byte of the serial frame. When deselected, the frame information of the CAN won’t be converted into the serial frame. 6.5 WHETHER CAN FRAME ID IS TRANSMITTED IN UART
This parameter is exclusively used in “Transparent Conversion” mode. When selected, the converter will include the frame ID of the CAN message before the frame data in the serial frame, following the frame information (if frame information conversion is allowed). When deselected, the CAN frame ID won’t be converted.
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7. UART PARAMETER SETTING
Baud rate: 1200~406800 (bps) UART parity method: no parity, even, odd Data bit: 8 and 9 Stop bit: 1, 1.5 and 2

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8. CAN PARAMETER SETTING

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This part introduces how the converter CAN set the baud rate, CAN send ID, frame type and CAN filter of the converter. CAN baud rate supports 10kbps~1000kbps and also supports user’s definition. Frame types support extended frames and standard frames. The frame ID of CAN is in hexadecimal format, which is valid in “transparent conversion” mode and “transparent conversion with ID” mode, and sends data to the CAN bus with this ID; This parameter is not valid in Format Conversion mode.
There are 14 groups of CAN receiving filters, and each group consists of “filter type”, “filter acceptance code” and “filter mask code”.

8.1 CAN BAUD RATE SETTING
Most common baud rates have been reserved in the list: this device does not support customization.

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8.2 CAN FILTER SETTING

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14 groups of CAN receiving filters are disabled by default, which means the data of the CAN bus are not filtered. If users need to use filters, you can add them in the configured software, 14 groups can be added.

Filter mode: optional “Standard Frame” and “Extended Frame”. Filter acceptance code: used to compare the frame ID received by CAN to determine whether the frame is received in hexadecimal format. Filter mask code: used to mask some bits in the acceptance code to determine whether some bits of the acceptance code participate in the comparison ((bit is 0 for non-participation, 1 for participation), in hexadecimal format. Example 1: Filter type selected: “Standard Frame”; “Filter Acceptance Code” filled with 00 00 00 01; “Filter Mask Code” filled with 00 00 0F FF. Explanation: As the standard frame ID consists of only 11 bits, the last 11 bits of both the acceptance code and the mask code are significant. With the mask code’s final 11 bits all set to 1, it means that all the corresponding bits in the acceptance code will be considered for comparison. Therefore, the mentioned configuration allows the standard frame with an ID of 0001 to pass through. Example 2: Filter type selected: “Standard Frame”; “Filter Acceptance Code” filled with 00 00 00 01; “Filter Mask Code” filled with 00 00 0F F0. Explanation: Similar to example 1, where the standard frame has only 11 valid bits, the last 4 bits of the mask code are 0, indicating that the last 4 bits of the acceptance code will not be considered
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for comparison. Hence, this configuration allows a group of standard frames ranging from 00 00 to 000F in ID to pass through.
Example 3: Filter type selected: “Extended Frame”; “Filter Acceptance Code” filled with 00 03 04 01; “Filter Mask Code” filled with 1F FF FF FF.
Explanation: Extended frames have 29 bits, and with the mask code’s last 29 bits set to 1, it means that all the last 29 bits of the acceptance code will be involved in comparison. Therefore, this setting enables the passage of the extended frame with an ID of “00 03 04 01”.
Example 4: Filter type selected: “Extended Frame”; “Filter Acceptance Code” filled with 00 03 04 01; “Filter Mask Code” filled with 1F FC FF FF.
Explanation: Based on the provided settings, a group of extended frames ranging from “00 00 04 01” to “00 0F 04 01” in ID can pass through.
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9. CONVERSION EXAMPLE

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9.1 TRANSPARENT CONVERSION
In transparent conversion mode, the converter promptly converts and sends the data received from one bus to the other bus without delay.
9.1.1 SERIAL FRAME TO CAN
The entire data of the serial frame is sequentially populated into the data field of the CAN message frame. Once the converter receives a frame of data from the serial bus, it immediately transfers it to the CAN bus. The information of the converted CAN message frame (the frame type section) and the frame ID are pre-configured by the user, and throughout the conversion process, the frame type and frame ID remain unchanged.

The data conversion follows the following format: If the length of the received serial frame is less than or equal to 8 bytes, characters 1 through n (where n is the length of the serial frame) are sequentially placed into positions 1 through n of the CAN message’s data field (with n being 7 in the illustration). If the number of bytes in the serial frame is more than 8 bits, the processor starts from the first character of the serial frame, takes the first 8 characters, and fills them sequentially into the data field of the CAN message. Once this data is sent to the CAN bus, the remaining serial frame data is converted and filled into the data field of the CAN message until all the data has been converted.

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For example, the CAN parameter setting selects “Standard Frame”, and the CAN ID is 00000060, note that only the last 11 bits of the standard frame are valid.
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9.1.2 CAN FRAME TO UART On the CAN bus message, it promptly forwards one frame upon receiving one frame. The data
format corresponds as shown in the diagram. During conversion, all the data present in the data field of the CAN message is sequentially
converted into the serial frame. If, during configuration, the setting “Whether CAN information is to be converted into serial” is
enabled, the converter will directly fill the “Frame Information” byte of the CAN message into the serial frame.
Similarly, if the setting “Whether CAN Frame ID is to be converted into serial” is enabled, all the bytes of the CAN message’s “Frame ID” will be filled into the serial frame.
For example, if “Convert CAN Message to Serial” is enabled but “Convert CAN Frame ID to Serial” is disabled, the conversion of a CAN frame to a serial format would be as depicted in the
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following diagram:
Serial Frame Format
07 01 02 03 04 05 06 07

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CAN message (Standard frame)

Frame

07

Information

00 Frame ID
00

01

02

03

Data

04

Division

05

06

07

9.2 TRANSPARENT CONVERSION WITH ID
Transparent conversion with ID is a specialized use of transparent conversion that facilitates users in constructing their networks more conveniently and employing custom application protocols.
This method automatically converts the address information from a serial frame into the frame ID of the CAN bus. By informing the converter about the starting address and length of this address in the serial frame during configuration, the converter extracts this frame ID and converts it into the frame ID field of the CAN message. This serves as the ID of the CAN message when forwarding this serial frame. When converting a CAN message into a serial frame, the ID of the CAN message is also translated into the respective position within the serial frame. It’s important to note that, in this conversion mode, the “CAN ID” setting in the “CAN Parameter Settings” of the configuration software is invalid. This is because, in this scenario, the transmitted identifier (frame ID) is populated from the data within the aforementioned serial frame.
9.2.1 UART FRAME TO CAN
Upon receiving a complete serial data frame, the converter promptly forwards it to the CAN bus.
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The CAN ID carried within the serial frame can be set within the configuration, specifying its starting address and length within the serial frame. The range for the starting address is from 0 to 7, while the length ranges from 1 to 2 for standard frames and 1 to 4 for extended frames.
During conversion, based on the pre-configured settings, all CAN frame IDs within the serial frame are entirely translated into the frame ID field of the CAN message. If the number of frame IDs within the serial frame is fewer than the number of frame IDs within the CAN message, the remaining IDs within the CAN message are filled in the order of ID1 to ID4, with the remaining one filled with “0”. The rest of the data undergoes sequential conversion as shown in the diagram.
If a single CAN message frame does not complete the conversion of the serial frame data, the same ID continues to be used as the frame ID for the CAN message until the entire serial frame has been completely converted.

Serial Frame Format

Address CAN

0

frame ID

Address 1 Data 1

Address 2

Data 2

Address 3

Data 3

Address 4

Data 5

Address 5

Data 6

Address 6

Data 7

Address 7

Data 8

……

……

Address (n-1)

Data n

CAN message 1 CAN message … CAN message x

Frame Information Frame ID 1
Frame ID 2

User configuration
00 Data 4
(CAN frame ID 1)

User configuration
00 Data 4
(CAN frame ID 1)

User configuration
00 Data 4
(CAN frame ID 1)

Data 1

Data …

Data n-4

Data 2

Data …

Data n-3

Data Division

Data 3 Data 5

Data … Data …

Data n-2 Data n-1

Data 6
Data 7 Data 8 Data 9

Data …
Data … Data … Data …

Data n

For example, the initial address of the CAN ID in the serial frame is 0, the length is 3 (in the extended
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WS-TTL-CAN
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Serial Frame Format

Data 1 Address 0 (CAN frame ID 1)

Data 2 Address 1 (CAN frame ID 2)

Address 2

Data 3

(CAN frame ID 3)

Address 3

Data 1

Address 4
Address 5 Address 6 Address 7 Address 8 Address 9 Address 10 Address 11 Address 12 Address 13 Address 14

Data 2
Data 3 Data 4 Data 5 Data 6 Data 7 Data 8 Data 9 Data 10 Data 11 Data 12

CAN message 1 CAN message 2

Frame

88

85

Information

Frame ID 1

00

00

Frame ID 2 Frame ID 3 Frame ID 4
Data Division

Data 1
(CAN frame ID 1)
Data 2
(CAN frame ID 2)
Data 3
(CAN frame ID 3)
Data 1 Data 2 Data 3 Data 5 Data 6 Data 7 Data 8

Data 1
(CAN frame ID 1)
Data 2
(CAN frame ID 2)
Data 3
(CAN frame ID 3)
Data 9 Data 10 Data 11 Data 12

9.2.2 CAN FRAME TO UART
If the initial address of the configured CAN ID is 0 in the serial frame and a length of 3 (in the case of extended frames), the CAN message and the result of converting it to a serial frame is shown below:

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Serial Frame Format
20
30 40 Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7

CAN message

Frame Information
Frame ID
Data Division

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10 20 30 40 Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7

9.3 FORMAT CONVERSION

Data conversion format as shown below. Each CAN frame includes 13 bytes, and they include CAN information + ID +data.

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9.4 MODBUS PROTOCOL CONVERSION Convert the standard Modbus RTU serial data protocol to the specified CAN data format, and
this conversion generally requires the editable CAN bus device message. The serial data must be compliant with the standard Modbus RTU protocol, otherwise it can not
be converted. Please note that CRC parity can not be converted to CAN. The CAN formulates a simple and efficient segment communication format to realize Modbus
RTU communication, which does not differentiate between host and slave, and users only need to communicate according to the standard Modbus RTU protocol.
The CAN does not require CRC checksum, and after the converter receives the last CAN frame, the CRC will be added automatically. Then, a standard Modbus RTU data packet is formed and sent
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to the serial port. In this mode, the [CAN ID] of the [CAN Parameter Setting] of the configuration software is
invalid, because the identifier (frame ID) sent at this time is filled by the address field (node ID) in the Modbus RTU serial frame.
(1) Serial frame format (Modbus RTU) Serial parameters: baud rate, data bits, stop bits and parity bits can be set via configuration software. The data protocol needs to conform to the standard Modbus RTU protocol. (2) CAN The CAN side designs a set of segment protocol formats, which defines designed a segmentation protocol format that defines a method for segmenting and reorganizing a message that is greater than 8 bytes in length, as shown below. Note that when the CAN frame is a single frame, the segmentation flag bit is 0x00.

Bit No.

7

6

5

4

3

2

1

0

Frame

FF

FTR X

X

DLC (data length)

Frame ID1

X

X

X

ID.28-ID.24

Frame ID2

ID.23-ID.16

Frame ID3

ID.15-ID.8

Frame ID4

ID.7-ID.0 (Modbus RTU address)

Data 1

segmentation segmentation

flag

type

segmentation counter

Data 2

Character 1

Data 3

Character 2

Data 4

Character 3

Data 5

Character 4

Data 6 Data 7 Data 8

Character 5 Character 6 Character 7

The CAN frame message can be set by the configuration software (remote or data frame; standard or extended frame).
The transmitted Modbus protocol starts from “Data 2” byte, if the protocol content is more than 7 bits, and the rest of the protocol content is converted in this segmented format until the conversion is
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complete. Data 1 is segmentation control message (1 byte, 8bit), and the meaning as shown below:
Segmentation Flag The segmentation mark occupies one bit (Bit7), and indicates whether the message is a
segmented message or not. “0” indicates a separate message, and “1” indicates a frame in a segmented message.

Segmentation Type The segmentation type occupies 2 Bits (Bit6, Bit5), and indicates the types of the report in this
segment report.

Bit Value (Bit6, Bit5)
00
01 10

Description The first segmentation
The middle segmentation The last segmentation

Note
If the segmentation counter includes the value=0, and then this is the first segmentation.
Indicates this is the middle segmentation, and there are multiple segmentation or there are no middle segmentation. Indicates the last segmentation

Segmentation Counter Occupies 5 bits (Bit4-Bit0), used to distinguish the serial number of segments in the same frame
Modbus message, enough to verify whether the segments of the same frame are complete. (3) Conversion Example: The serial port side Modbus RTU protocol (in hex). 01 03 14 00 0A 00 00 00 00 00 14 00 00 00 00 00 17 00 2C 00 37 00 C8 4E 35 The first byte 01 is the Modbus RTU address code, converted to CAN ID.7-ID.0; The last 2 bytes (4E 35) are Modbus RTU CRC checksums, which are discarded and not
converted. The final conversion to CAN data message is as follows: Frame 1 CAN message: 81 03 14 00 0A 00 00 00 00

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Frame 2 CAN message: a2 00 00 14 00 00 00 00 00 Frame 3 CAN message: a3 00 17 00 2C 00 37 00 CAN message frame 4: c4 c8 The frame type (standard or extended frame) of the CAN telegrams is set via the configuration software; The first data of each CAN message is filled with segmented information (81, a2, a3 and c4), which is not converted into Modbus RTU frames, but only serves as acknowledgment control information for the message.
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The conversion principle of data from CAN side to ModBus RTU is the same as the above, after the CAN side receives the above four messages, the converter will combine the received CAN messages into a frame of RTU data according to the CAN segmentation mechanism mentioned above, and add CRC checksum at the end.
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References

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