Improving performance of X-USBDC (FTDI)

The X-USBDC is a USB to Serial Converter cable that allows connecting X-Series products to the computer's USB port. Inside the cable resides a chip manufactured by FTDI. FTDI chips are commonly used way to convert serial (RS232) signals to USB with drivers available on most contemporary operating systems.

The driver has a setting called Latency Timer that can be adjusted to improve the latency (responsiveness) of the device. However, most users of Zaber Motion Library don't need to be concerned with this as Zaber's firmware already has features designed to deal with communication delay. Streams and PVT Sequences both deliver continuous motion free of communication lag. It's worth noting that even after changing the Latency Timer the remaining latency causes delays between individual movements and the performance won't match that of Streams. If you need to read data from the device at a high (or precise) frequency, we recommend using Oscilloscope.

Lowering the Latency Timer reduces communication latency and increases bandwidth potentially up to twice the baseline. This can improve the performance of certain applications that intensively communicate with the device. We are not aware of any adverse effects of lowering the Latency Timer. The default value is 16 ms. The lowest possible value is 1 ms and is not recommended by FTDI's documentation. We recommend setting the value to 2 ms. Our tests confirmed that the value works well and yields no worse practical performance than 1 ms.

Select your operating system to see instructions on how to change Latency Timer.

On Windows, go to the Device Manager, find your serial port, and right-click on Properties. Then select Port Settings tab, click Advanced, and change the Latency Timer value.