For professionals in auto repair and vehicle diagnostics, understanding the communication protocols and settings of On-Board Diagnostics II (OBDII) systems is crucial. When working with tools like Freematics OBDII devices, one key aspect is the Freematics Obdii Baud Rate, which dictates the speed of serial communication. This article delves into the significance of baud rate in OBDII communication, particularly within the context of Freematics emulators, and explores the essential AT commands for managing these settings.
What is Baud Rate in OBDII Communication?
In serial communication, baud rate refers to the number of signal changes per second. In the context of OBDII, it defines the speed at which data is transmitted between diagnostic tools (like a Freematics device) and the vehicle’s electronic control units (ECUs). A higher baud rate allows for faster data transfer, which is essential for real-time diagnostics and data logging.
Freematics OBDII emulators, designed for testing and development purposes, utilize a specific baud rate for their serial interface. Understanding this rate is fundamental for establishing proper communication and effectively using AT commands to interact with the emulator.
Freematics OBDII Emulator Default Baud Rate
The default baud rate for serial communication with Freematics OBDII emulators is 38400 bps (bits per second). This setting is pre-configured to ensure reliable communication across various platforms and applications. It’s important to note this default baud rate when setting up your communication interface, whether you are using a serial terminal, a custom application, or other diagnostic software.
This standard baud rate allows for a balance between communication speed and robustness, ensuring that data is transmitted accurately without overwhelming the system, especially in environments where signal integrity might be a concern.
Essential AT Commands for Freematics OBDII Emulators
Freematics OBDII emulators use a set of AT commands, similar to Hayes command set, to control their functions and simulate different OBDII protocols. While there isn’t a specific “AT command” to directly change the baud rate in the provided documentation, understanding the available commands is crucial for configuring and using the emulator effectively. These commands are sent via the serial interface at the default 38400 bps.
Here’s a breakdown of key AT commands, categorized for clarity:
Initialization and Reset Commands
- ATZ: Initializes the emulator. This command resets the emulator to its default state and responds with the emulator’s name and version, confirming communication.
- ATR: Resets the emulator. Similar to ATZ, this command resets the system and provides the emulator’s identification.
Echo Control
- ATE0/ATE1: Turns character echoing off (ATE0) or on (ATE1). Echoing is useful for debugging serial communication, as it displays the commands you send back to you. The emulator responds with “OK” to confirm the command.
Protocol Configuration
- ATBUS [Protocol]: Changes the simulated OBDII protocol. This command is vital for testing different diagnostic scenarios. Supported protocols include various CAN bus speeds and standards like KWP2000, ISO9141, and J1850.
- Examples:
ATBUS CAN_11B_500K(sets to 11-bit CAN bus at 500Kbps)ATBUS KWP2000_FAST(sets to KWP2000 Fast protocol)
- Response: “OK” if successful, “ERROR” otherwise.
- Examples:
Diagnostic Trouble Code (DTC) Management
- ATSET DTC=[Mode 03 Trouble Codes]: Sets Mode 03 DTCs (Diagnostic Trouble Codes). Mode 03 codes are current, active fault codes.
- Example:
ATSET DTC=P0105,P0106(sets DTCs P0105 and P0106)
- Example:
- ATSET DTC7=[Mode 07 Trouble Codes]: Sets Mode 07 DTCs (Pending DTCs). Mode 07 codes are intermittent or pending fault codes.
- Example:
ATSET DTC7=P0105,P0106
- Example:
- ATSET DTCA=[Mode 0A Trouble Code]: Sets Mode 0A DTCs (Permanent DTCs). Mode 0A codes are permanent fault codes that cannot be cleared by simply clearing codes.
- Example:
ATSET DTCA=P0105,P0106
- Example:
- ATCLR DTC: Clears all set DTCs. This command simulates clearing diagnostic trouble codes in a vehicle.
Parameter Identification (PID) Control
- ATSET [PID]=[Value] / ATSET [PID]=[A],[B],[C],[D]…: Sets the value of a Mode 01 PID (Parameter ID). PIDs are used to request specific data parameters from the vehicle.
- Examples:
ATSET 010C=2000(sets RPM (PID 010C) to 2000 RPM)ATSET 010C=0x31,0x64(sets RPM using raw hex data)
- Examples:
- ATGET [PID]: Retrieves the current value of a Mode 01 PID.
- Example:
ATGET 010C(requests the current RPM value) - Response: Raw HEX data of the PID.
- Example:
Vehicle Identification Number (VIN) and Calibration Data
- ATGET VIN: Reads the emulator’s VIN (Vehicle Identification Number).
- ATSET VIN=[Vehicle Identification Number]: Sets the VIN (PID 0902). Requires a 17-digit VIN string.
- ATSET CID=[Calibration ID]: Sets the Calibration ID (PID 0904).
- ATSET CVN=[Calibration Version Numbers]: Sets Calibration Version Numbers (PID 0906).
VIN and Ignition Emulation
- ATVIN0 / ATVIN1: Disables (ATVIN0) or enables (ATVIN1) VIN response.
- ATACC0 / ATACC1: Emulates ignition OFF (ATACC0) or ON (ATACC1). Note that this does not simulate voltage changes associated with ignition switching.
Debug Information
- ATINF0 / ATINF1: Disables (ATINF0) or enables (ATINF1) debug information output. Useful for troubleshooting communication and command execution.
Conclusion
Understanding the freematics obdii baud rate of 38400 bps and the associated AT command set is essential for anyone working with Freematics OBDII emulators. While the baud rate is fixed, the extensive AT command set allows for comprehensive control over protocol simulation, DTC management, PID manipulation, and vehicle data emulation. By mastering these commands, automotive professionals can effectively utilize Freematics emulators for diagnostics development, testing, and training purposes, ensuring robust and reliable OBDII system interactions.
