OBDII 160 Baud Rate Aliasing for Enhanced Data Logging

Connecting a data logger to your vehicle’s OBDII port often involves dealing with baud rate discrepancies. This article focuses on aliasing the standard OBDII 9600 baud rate to achieve a more accurate 8192 baud rate for improved data logging using an FTDI chip. This process enhances communication efficiency and reduces error packets, leading to cleaner and more reliable data.

While OBDII typically uses a 9600 baud rate, certain applications, like data logging with specific tools, require a precise 8192 baud rate. A direct connection at 9600 baud results in an efficiency of only 85.33%, leading to potential data loss and errors. By aliasing the 9600 baud rate to 8192 baud, you can achieve near-perfect efficiency (99.99%), significantly improving data integrity.

Understanding Baud Rate Aliasing with FTDI Chips

FTDI chips, commonly found in OBDII adapters and data loggers, allow for baud rate customization through registry modifications. The FTDI driver (FTDIPort.INF) contains a configuration string that defines standard baud rates. Modifying specific hexadecimal values within this string enables aliasing, effectively remapping one baud rate to another.

This modification involves accessing the Windows Registry and altering the ConfigData binary value associated with your FTDI device. This value holds the hexadecimal representations of various baud rate divisors. By calculating the correct divisor for 8192 baud and replacing the corresponding 9600 baud values, you can achieve the desired aliasing.

Implementing OBDII 160 Baud Rate Aliasing

Disclaimer: Modifying the Windows Registry can potentially harm your system. Proceed with caution and at your own risk.

1. Identify Your FTDI Device: Connect your data logger and open Device Manager. Locate the device under “Ports (COM & LPT),” right-click, and select “Properties.” In the “Details” tab, choose “Device instance path” from the “Property” dropdown to find your FTDI device ID (e.g., FTDIBUSVID_0403+PID_6015+DN05K0BRA000).

2. Access the Registry Editor: Open the Registry Editor (RegEdit) by searching for it in the Start Menu.

3. Navigate to FTDI Configuration: Locate the ConfigData binary value within the registry by following this path, substituting your specific device ID: HKEY_LOCAL_MACHINESYSTEMCurrentControlSetEnumFTDIBUS{Your Device ID}000Device Parameters.

4. Modify the ConfigData Value: Double-click ConfigData to modify it. Find the hexadecimal bytes representing the 9600 baud rate (typically 38,41). Replace these with 6E,81, the calculated values for 8192 baud (derived from the formula: 3000000 / 8192 = 366.21 ≈ 366.25, converting to hexadecimal and accounting for the sub-divisor).

5. Restart Your System: Save the changes, close RegEdit, and restart your computer for the changes to take effect.

After restarting, your data logger should communicate at the aliased 8192 baud rate when set to 9600 baud in your software. This process significantly improves data logging accuracy and reduces errors associated with baud rate mismatches. Note that the displayed baud rate in device manager will still show 9600, but the actual communication will occur at 8192 baud.