E-Prime Knowledge Base

1835 - INFO: Use of DB9 Serial to USB adapter within E-Prime

If you are using a computer that does not have a serial port, you can purchase a DB9-USB converter cable for use with devices that use serial communication. We have confirmed that these adapters do work with the SRBox and FOBRS in E-Prime and provide accurate timing even on the slowest of machines.

It is vital that serial-to-USB cables use the latest drivers available. To do this, visit each cable manufacturer's website or use Windows Update to download updated drivers.

Recommended: Prolific cable, model ICUSB232DB25

DB9-to-USB Adapter Brand Compatibility:

Adapter Brand Compatible With E-Prime?
BAFO Yes
ATEN Yes
Prolific Yes
FTDI Yes - requires configuration*
Belkin some reported problems
Keyspan No


*The FTDI brand serial-to-USB adapter requires a change in its latency timer in order to establish a polling rate that will deliver its best results. To do this, plug in the cable, install the latest drivers possible, go to Start, right click on the 'Computer' icon, go to 'Manage', then 'Device Manager', then expand the 'Ports' dropdown, right click on 'USB Serial Port', select 'Properties', then the 'Port Settings' tab, 'Advancedů' button, and change 'Latency Timer (msec):' from '16' to '1'. Press 'OK' to continue.

Average latencies when using a SRBox or FOBRS with an adapter cable:

Adapter Device Duration Average Latency Mean STDDEV Max Min
Prolific FOBRS 10 2.48 12.48 0.56 14 11
Prolific SRBOX 10 2.56 12.56 0.72 14 11
Prolific FOBRS 50 2.52 52.52 0.73 54 51
Prolific SRBOX 50 2.56 52.56 0.61 54 51
ATEN FOBRS 10 2.4 12.4 0.73 14 11
ATEN SRBOX 10 2.67 12.67 0.67 14 11
ATEN FOBRS 50 2.44 52.44 0.56 54 51
ATEN SRBOX 50 2.45 52.45 0.8 54 51
FTDI-Default FOBRS 10 6.93 16.93 6.5 29 11
FTDI-Default SRBOX 10 6.59 16.59 5.61 29 12
FTDI-Default FOBRS 50 3.33 53.33 0.8 55 51
FTDI-Default SRBOX 50 3.64 53.64 0.81 56 52
FTDI-PollChange FOBRS 10 3.33 13.33 0.73 15 12
FTDI-PollChange SRBOX 10 3.45 13.45 0.69 15 12
FTDI-PollChange FOBRS 50 3.38 53.38 0.68 55 52
FTDI-PollChange SRBOX 50 23.72 73.72 202.38 2067 52
N/A XKEYS (FOBRS native USB) 10 42.92 52.92 2.44 58 48
N/A XKEYS (FOBRS native USB) 50 42.82 92.82 3.23 99 87


Timing tests from May 2011. Test results using E-Prime 2.0.8.90. The testing paradigm involved sending a parallel port pulse at the onset of an object from the E-Prime Experiment Station to the E-Prime Timing Station, which waited the specified delay. Then, the Timing Station sent a parallel port pulse to the test device (SRBox or FOBRS) that responded via the adapter cable to the Experiment Station's object's Input Mask. The latency is the recorded RT minus the delay.

Legacy timing differences using the SRBOX with a standard serial port:

Machine Operating System Serial Port Type Reaction Time Delay (Mean) Reaction Time Delay (StdDev)
Dell 8200 (2GZ) Windows XP Standard UART 1.73 ms 0.68
Dell 8200 (2GZ) Windows XP USB-DB9 Cable 1.85 ms 0.66
Dell 8400 (3GZ) Windows XP Standard UART 1.81 ms 0.61
Dell 8400 (3GZ) Windows XP USB-DB9 Cable 1.99 ms 0.66


Timing tests from E-Prime 1.2, March 2006. The ATEN UC232A USB to DB9 serial adapter cable was used. Test results using E-Prime 1.2 with the BBTK triggering a response to the E-Prime subject computer.

To connect the cables and add the SRBox to your experiment:

1. Turn your computer off.

2. Attach the cables to the SRBox. First, connect the large end of the serial cable to the back of the SRBox where it is marked 'Serial Cable'. Next, connect the power cable to the back of the box and then plug it into an outlet. There is no on/off switch so plugging it in is the only way to ensure that the SRBox is on.

3. Connect the other end of the SRBox's cable to the DB9 side of the USB adapter. This is the side that will allow you to screw the two cables together if applicable. Once they are securely connected, plug the USB end of the cable into one of the USB ports on your computer.

4. Turn the computer on and make sure that the device is recognized. You may need to use Windows Update to update the cable's drivers so that Windows will recognize it. It should be using COM ports 1, 2, 3, or 4. For specific instructions on how to check your port number, please see below.

5. Once you know your port number and have ensured that it is one of the four recognized ports, you can configure E-Prime to communicate with your SRBox. The SRBox can be added by double-clicking the Experiment Object (at the top of the Structure view) to open its property pages, then clicking the Devices tab. Click the Add button and select the SRBox. Click on the small picture of the SRBox to highlight the word 'SRBOX', making sure not to uncheck the box next to it. Click 'Edit...' and make sure that the number after the word 'Port' matches the port number that you saw in device manager. Click 'Ok' twice to exit.

6. Enable the SRBox as an Input Mask on an object. To do this, double-click on the object on which you would like to add the SRBox as an Input Mask and click on the icon for the object's Property Pages. Once the Property Pages are up, select the Duration/Input tab and click "Add..." to add the SRBox as the Input Mask.

7. Test that your SRBox is responding properly. If you would like a test experiment, try the SRBOX Sample For E-Prime on our website: http://www.pstnet.com/hardware.cfm?ID=102.

To verify or change your port settings so that you are using COM 1-4 as supported by E-Prime:

1. Connect the DB9-USB converter to the USB port
2. Click Start - Control Panel - System
3. Click the Hardware tab on the System Properties page
4. Click Device Manager
5. Click on the "+" next to "Ports" to view the listing of ports used by your machine.
If the USB port is not listed as COM 1-4, then you will need to manually change the port setting. In some cases the COM port gets assigned as COM 5 or higher which is not an option for the SRBox in E-Prime.



6. To change the port setting, Right click on the USB port that you are using for the SRBox and select Properties
7. Select Port Settings tab
8. Click on Advanced button
9. Use the drop down box next to COM Port Number to change it to COM 1-4.
10. Click OK and Close the Control Panel

You will see the change the next time you follow the above steps to verify the port setting.



This topic was created on:
Updated on 1/9/2004 7:47:00 PM (GMT)

This topic was last updated on:
Updated on 7/2/2012 9:16:00 PM (GMT)



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