A company named Elexol makes a second generation serial-to-USB port adapter called the USBMOD3. Many newer notebook computers are being built with USB ports, but without the classic serial ports. Here are the pin connections needed to connect a USBMOD3 to the datalogging port of a Honda ECU:

Pin 4 (Vcc) should be wired to Pin 8 (Reset In) since an external device doesn't need to reset the device.

Pin 9 (Enumeration Power) should be wired to Pin 10 (Reset Out) for bus powered operation per the user's manual.

Pin 12 (VIO) should be wired to Pin 13 (V+) to power the UART IO properly.

Pin 18 (Power Control) should be wired to ground to select bus powered operation per the user's manual. I wired the ground pins (2, 16 and 29) together (May not be needed since they are wired together in the module) and wired them to the shield of the cable which is wired to ECU CN2 Pin 1, which is ECU ground.

Pin 23 (Data Set Ready) should be wired to Pin 24 (Data Terminal Ready) for modem control handshaking.

Pin 25 (Clear To Send) should be wired to Pin 26 (Request To Send) for modem control handshaking.

Pin 27 (RXD) should be temporarily wired to Pin 28 (TXD) for a loopback test. I used a clip-lead.

You can get the USBMOD3 driver from FTDI.

After you plug in the USBMOD3, you can test that it is recognized by your MS Windows computer by checking Device Manager under Ports to see which COMn: port is mapped to which USB port. You can set the serial port settings such as baud rate and parity by opening the Properties window and selecting the Port Settings tab.

You can test the USBMOD3 by opening Windows Hyperterminal, and pointing it at the proper serial port, the one that you saw in Device Manager. With Pins 27 and 28 connected fot the loopback test, everything you type in Hyperterminal will echo to the Hyperterminal window on your PC.

After that test is successful, all you need to do is connect Pin 29 (GND) to the ECU ground signal (ECU CN2 Pin 1), connect Pin 27 (RXD) to the ECU TXD signal (ECU CN2 Pin 2) and connect Pin 28 (TXD) to the ECU RXD signal (ECU CN2 Pin 4) as described at ECU Control under the How to Mod my ECU link. (Thanks Nicolas)

I wired my CN2 connector to a DIN connector on the side of the ECU case and then made a dongle for the USBMOD3 unit. You can see pictures here: http://www.classictiger.com/HondaCRX/usbmod3/

-- markolson - 29 Oct 2004

Late note: I triple, triple checked that I had the data signals crossed so each transmitter talked to a receiver, and I still screwed it up. If you do all this, and it still doesn't work, swap the transmit and receive data signals at one end, and try it again. Also, make sure you understand how the datalogging software works before you assume your circuit is not working. See Debugging Data Logging for details. -- markolson - 01 Jan 2005