Vetra Systems Corporation
KVM solutions that work
Vetra Systems manufactures a complete line of KVM products and solutions

USB-331 RS-232 to USB Keyboard Protocol Converter Convert RS-232 ASCII data to USB Keyboard input with the USB-331 "SmartPipe"



USB-331: Converts RS-232 input data to USB Keyboard codes.

Same functions as above, but is assembled PCB only (has no housing). Size of the PCB is 4.1 in x 4.785 in (10.4cm x 12.15 cm). Click (here) for detailed PCB dimensions.

All prices subject to change without notice.
For International Representatives click here.

Vetra USB Protocol Converters can be used in many applications to connect RS-232 data sources to PCs, iMACs and other computers equipped with an USB port. The RS-232 ASCII coded data appears as keyboard input to the PC. Industrial control, point-of-sale, bar code readers, instrumentation, structured test, compatibility test, and data acquisition are some of the many areas where Vetra Protocol Converters have found effective application. The USB-331 is powered by the PC's USB port, so no external power supply is required.

To connect additional keyboards, use a hub, another USB port on the PC, or use the Vetra USB-335 protocol and code converter with on-board 2-port hub.

Compared to the VIP-335 Protocol Converter for PC PS/2 keyboard input, the USB-331 takes advantage of the higher input rate of the standard USB keyboard input, which can be 750 characters per second. The available Extra Speed Option of the USB-331 raises the input rate to 3000 characters per second. Burst-oriented applications, such as bar code wands and bar code readers are likely to benefit from the high USB character rate. For an Application Note with more information on character rates click here for HTML format or here for PDF format.


The USB-331 SmartPipe™ Protocol and Code Converter allows RS-232 data to be fed directly into a USB port as keyboard data. The standard ASCII code set, common in RS-232 applications, does not correspond to the codes of the standard USB keyboard, requiring translation between ASCII and USB keyboard codes. The Vetra USB-331 Protocol Converter performs these ASCII code to USB keyboard code translations. Additional keyboards can be connected through an unused USB port on the computer, or via a hub. Or, use the USB-335 model with an on-board 2-port hub.The connection of a standard keyboard is optional and not necessary for the USB-331 to operate.

Code Conversion for the USB-331:

The USB-331 SmartPipe™ translates ASCII codes to equivalent USB keyboard codes as shown in the "ASCII to USB Key Code Translation" Table. Note that the table contains more codes than the standard ASCII set. These codes have been added to bring the functionality of keyboards used with PCs and iMACs into the ASCII world. Simulation of simultaneous depression of some keys is possible using the separate make and break codes for the Control, Shift, Alt and Window keys, both left and right. For instance, to simulate the Left Alt and F1 keys combination, hex codes 83, A0, 93 should be sent.

In addition to code translation, the protocol and code converter also converts voltage and protocol from the asynchronous RS-232 protocol to the USB 2.0 compliant HID device keyboard protocol.

The male DB-9 connector on the USB-331 receives RS-232 data on pin 2, and controls Clear-To-Send (CTS) on pin 7. Pin 5 is ground. For an Application Note with more information on need for CTS and throughput rates in HTML format click here, or in PDF format. The USB-331 uses the following RS-232 format: 1 start bit, 1 stop bit, 8 data bits, and no parity.
There are six baud rates to choose from: 300, 1200, 2400, 4800, 9600 and 19,200 baud.

For a copy of Adobe's Acrobat® Reader


  • Designed and manufactured in the USA for use around the world
  • Backed by a Limited 3 Year Warranty
  • Converts RS-232 ASCII data to USB 2.0 compliant keyboard data
  • Extra Speed Option has four times faster throughput than a standard USB keyboard
  • Allows connection of additional keyboards to another USB port or via hub
  • Custom versions available



A standard USB Type A-B cable, provided with the unit, is used to connect the USB-331 converter to a USB port of the PC or MAC (no cable is provided with the USB-331-OEM). The USB port can be directly on the computer or on a hub connected to the computer. A cable terminated in a standard DB-9 female connector is required to interface RS-232 data to the converter. Vetra offers a selection of DB-9 cables, see Accessories.


Dimensions for the USB-331 Protocol Converter are 1.5 in H x 5.08 in W x 5.25 in D (3.81 cm x 12.90 cm x 13.34 cm). For dimension data for the USB-331-OEM click here. The USB-331 is powered by the PC's USB port, so no external power supply is required. The housing is molded of black GE Cycolac-T, a high impact ABS material, and is internally shielded with an acrylic base nickel coating for RFI attenuation. Front and rear panels are fabricated from .062 in thick aluminium and finished with low gloss black paint. FCC and CE marked. Shipping weight is less than 2 lbs per unit.

 Environmental Operating Temp:
Storage Temp:
5 to 104 deg. F (-15 - 40 deg. C) 
-4 to 122 deg. F (-20 - 50 deg. C)
 Supported Hardware Computer:
Any computer with a USB port
The USB-331 Protocol Converter uses technology protected by US Patent 7,299,309
SmartPipe is a trademark of Vetra Systems Corporation
Copyright © 1995-2010 by Vetra Systems Corporation, All Rights Reserved

For user instructions in PDF format.

For a copy of Adobe's Acrobat® Reader".


 All Vetra Systems products are proudly designed and manufactured in the USA for use around the world in enterprise mission-critical applications and are backed by a
Limited 3 Year Warranty

[ Home ]

[ Products ]

[ About Us ]

[ Site Map ]

[ Contact Us ]

[ Order Info ]

[ What's New ]

[ KVM Switches ]

[ Dual-Head KVM Switches ]

[ Touch Screen Products ]

[ Video Products ] 

[ KVM Splitters ]

[ PC Keyboard Encoders ]

[ Keyboard & Mouse Terminators ]

[ KVM Extenders ]

[ Safe Computing Products ]

[ Foot-operated Devices ]

[ Protocol Converters ]

[ Accessories ]

 Vetra Systems Corporation logo

 VETRA Systems Corporation
275 Marcus Blvd. Ste-J, Hauppauge, NY 11788-2022 USA
Toll Free 1-800-537-9296
Tel: 631-434-3185 Fax: 631-434-3516 e-mail: