Using RS232 Devices with USB Ports


There are a host of RS232 based data acquisition and control products available on the market.   These devices can be used with Universal Serial Bus ( USB ) ports using our new ADU series of USB data acquisition and control interfaces.  The ADU USB data acquisition and control interfaces feature a variety of I/O accessed via a  USB port. All ADU products also feature an auxiliary RS232 port that allows access to RS232 based devices. Visit our Progarmming page to view tutorials on sending and receiving ASCII data via COM ports, or making API calls to USB devices,  in virtually any programming language.

For example, the ADU200 USB Relay I/O Interface can be use to provide a USB to RS232 conversion while adding additional relay I/O to an application

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The following illustration shows how an ADU200 can be used to connect an ADR2205 RS232 Relay I/O Interface to a USB based host computer.

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For more details on these unique products view the  ADU200 USB Relay I/O Interface product data sheet and the on-line SDK in the programming section of this site.

USB to RS232 Converters

Another method of connecting RS232 devices to a USB based host is to use a USB to RS232 converter.  These devices connect to the host computer USB port via a USB cable and provide a DB25 or DB9 serial port for use with RS232 devices.  The example will demonstrate how the ADR2200 RS232 Relay I/O interface can be used to provide relay I/O to a USB equipped host computer.

ADR2200 RS232 Relay I/O Interface

Getting Started

To connect an ADR2200 to a USB based computer, all that is required is a USB to RS232 converter , a standard A-B USB cable, an RS232 cable and the ADR2200 target device. The host computer must be running Windows 98SE, 2000 or XP operating system.   There are a host of USB to RS232 devices available on the market and we have selected the Peracom US1000A for our example.

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Figure 1 A: Peracom US1000A USB to Serial Converter  (Available from USBSTUFF for $64.95US.)

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Figure 1 B: USB to Four RS232 Port Adaptor ( Edgeport/4  from Inside Out  Networks.)

Note: A four port version ( Figure 1B ) is available from  Inside Out  Networks that allows four RS232 ports to be derived from a single USB port. We have extensivelly tested this unit and recommend it for systems requiring use of many RS232 peripherals, such as POS ( Point-Of-Sale ) applications.

Installing the USB to RS232 Converter

The USB to RS232 converter is shipped with a Windows driver disk . When the converter is connected to the Windows based host computer,  Windows will display the "Found New Hardware" screen and will prompt the user for a driver for the device.  With the driver disk installed in drive "A", select the "Have Disk" option and browse the driver disk to the appropriate driver.  Once installed, the USB converter will be assigned the next available COM port on the host computer. To verify the proper set-up, open the "System" icon in the "Control Panel" and click on the "Device Manager" tab. Under "Ports", there should now be a new COM port labeled "USB Serial Port". ( See Figure 2. )

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Figure 2: USB Serial Port Configured as COM3

Writing Application Software

We are now ready to write data acquisition application software to access the ADR2200 RS232 Relay I/O interface connected to the USB to RS232 converter. Since the USB to RS232 converter is configured as an actual COM port, the application software can access the ADR2200 as if it were connected directly to the host computer through the specified COM port.  Programs can now be written in Visual BASIC, Visual C++, TestPoint or LabVIEW. ( click on links for specific examples )

Adding More Data Acquisition Capabilities

The ADR2200 RS232 Relay I/O interface is one in a family of serial data acquisition devices that are manufactured by Ontrak Control Systems Inc. All ADR2000 series devices feature daisy-chain capabilities allowing additional relay I/O, analog I/O, digital I/O , PWM outputs and event counters to be added to the application.  The devices are daisy-chained via a simple 2 or 4 wire connection allowing up to 10 interfaces to be connected to a single USB to RS232 converter device. Figure 3 shows how an ADR2200 could be daisy-chained with an ADR2000A data acquisition interface

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Figure 3: USB Data Acquisition using ADR2200 and ADR2000A