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Questions? Custom builds? We build and support all of our boards.
If you have a special application, we may already have a solution for you.
Give Ron a Call at 513-874-4796 or 513-638-0228 for additional information.
USB44T: USB to RS485 2 Wire Half Duplex or RS422 4 wire full Duplex Serial Converter


USB44T with Box

USB44T Label

"Let me spin a very large
RS485 network for you!"


Product Features

  • This auto transmit unit features bi-directional serial conversion from USB to RS485(2 wire half-duplex), or RS422(4 wire full duplex).

  • A group of jumpers enable the user to customize this device as an RS485 or RS422 converter. and configure the transmit bias and termination resistors. Refer to the schematic for details.

  • Optimized for non-isolated office/indoor point to point or multi-drop systems. We do not recommend this unit for outdoor sign application. The IUSB44T or IUSB24AT are better suited for that environment.

  • Transparent to all standard asynchronous formats and data rates supported by the USB interface, up to 921.6 Kbps. No jumpers or settings required. 

  • In RS485 mode, fast auto turn-around, from transmit to receive mode, requires no software delays and eliminates timing problems and data collisions. We pioneered and perfected this leading edge technology.

  • The RS485 driver allows 32 standard loads at 4000 ft. at data rates up to 921.6 Kbps.

  • Isolation resistors and a transcient suppressor bridge help protect the device from destructive electrical noise often found in industrial environments. The SP491EEP driver has high ESD tolerance.

  • Edge mounted LEDs display power and data activity at the RS485/RS422 interface.

  • Broad environmental range. Temperature: 0C to +70C(32F to +158F). Humidity: 10 to 90% RH(non-condensing)

  • Four(4) easy mount through hole standoffs, which accept #6 hardware, are provided on the circuit board.

  • User connections are a USB type B receptacle, and a 5 position removable screw terminal strip for the RS485/RS422 port. There is no external power connector. Device power is obtained through the USB port.

  • The required "Virtual Com Port" USB driver, for the host computer, is available from www.ftdichip.com under "Drivers". This web site provides drivers for most host operating systems. Some OS's will automatically search for, find, and install the appropriate software/driver. 

  • Accessories available are an enclosure, and a USB cable(6 ft USB type A plug to USB type B plug).

  • Conformal Coating, cable, and connectors, are factory options. Contact us for options help.

  • We feature a family of other similar USB isolated/non-isolated converters that may fit your needs. Check out the USBA4, IUSB24AT, and IUSB44T 

  • R E Smith Inc makes a wide variety of isolated converters that address the electrical noise problems that contribute to unreliable communications, and product failure.  If what you see here is not exactly what you need, don't hesitate in calling us at 513-874-4796.

  • We also have a new series of Converters and Repeaters that extend the RS485 communications distance far beyond conventional limits. Contact us for information on these leading edge problem solvers.

  • WARNING: Do NOT connect this device to a telephone system under any circumstances. Damage could result to the circuit board and/or your telephone system.

About R E Smith, Inc.

R E Smith, Inc. engineers and manufactures a comprehensive line of isolated and non-isolated converters, repeaters, multiport repeater hubs, fiber optic based products, and I/O boards. All our products are designed, built, tested, and shipped from our facility in the Greater Cincinnati Ohio area. We ship small quantities of most products from stock the same day, and larger quantities in a few business days.

We listen to you. We are customer driven. Many of our products were developed and improved due to suggestions and feedback from our word-wide customer base. They are being used at the South Pole, at the bottom of the sea, at the edge of space, and everywhere in between. Typical uses are very large networks, monitor and control of elevators, machinery, lighting, security, fire and alarm, access, cameras, military ground support, and much more. We provide free support, no-argument warranty repairs, and recommendations for your application. Challenge us with your communications problem. We may already have the solution. If your system keeps failing, or is unreliable, we have isolated, doubly isolated, noise resistant, cost effective, and proven solutions for difficult environments.

Related Files:

pdf icon USB44TRevA.pdf Unit schematic Rev A


USB: USB type B receptacle
RS485/RS422: 5-position removable screw terminal strip.
Power: Provided by the host device through the USB port.
LEDs Power(yellow) and RS485 data activity(TX: red, RX: green)
Bias: Transmitter: 470 Ohm pull-up and pull-down (jumper selectable)
Receiver: Weak pull-up and pull-down(39K Ohms)
Termination: Transmitter: none
Receiver: 150 Ohm (jumper selectable)
Protection: SP491EEP Driver with built in ESD tolerance, series resistors, and transcient suppressor bridge


Distance: Up to 4000 ft. (1220 meters)
Operation: USB to 2 wire half-duplex RS485
Format: Asynchronous data with any combination of bits, parity, and stop (auto mode)
Speed: Up to 921.6 Kbps
Environmental: 0C to +70C ambient, 10-90% RH(non-condensing)
Supply Voltage: +5VDC Provided by the host device through the USB port
Power: Under 1/2 Watt(typical) + external load
Size: 2.50" X 2.00" X 0.9" (PC Board), with connectors: 2.50" X 2.15"
Mounting: 4 Holes at 2.00" X 1.50" (built-in standoffs for #6 hardware)

Options and Ordering Information:

USB44T: $109.00 ea. (Circuit board only)
Enclosure: $8.00 ea. (small)
Cable: $4.75 ea (6ft USB type A Plug to USB type B Plug)

This is the complete order number for the USB44T with all available options:

USB44T with all options (USB cable and enclosure): Order Number: USB44T-B6AB @ $121.75 ea. (Qty. 1-9)

Need a different configuration or more information? Give Ron a Call at 513-874-4796 or 513-638-0228(Cell)

Webstore: USB44T

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