COM422-4 and COM485-4


  • Four independent, completely configurable, serial ports
  • Supports High-speed RS-422 (COM422-4) or Multi-drop RS-485 (COM485-4)
  • Supports RS-485 handshaking on-board without special drivers to support Windows and non-DOS programs (COM485-4 only)
  • Built-in support for local echo, line termination, and line bias supplies
  • Supports extended AT interrupts
  • Designed, made, supported, and manufactured in the US


Last updated on November 2, 2023, 6:30 pm


In Stock


ISA Bus RS-422/485 Communications Cards

The COM422-4 and COM485-4 are communication cards for RS-422 and RS-485 operation respectively. They feature four independent ports, buffered type 16550 UARTs, and automatic control to transparently enable/disable the transmission drivers as needed. There are two connector I/O options. The standard version includes a 25-pin male connector plus a “spider” cable with four DB9 male connectors. Optionally (pictured) two 9-pin male connectors are provided on the card mounting bracket, plus a second mounting bracket with two more 9-pin male connectors and ribbon cable for connections to headers on the card. (To specify this option, add S01 to the model number.)

These cards can receive inputs as low as 200 mV differential superimposed on common mode noise of maximum -7V to +12V. The transmitters feature thermal shutdown.

Continuous address selection is available individually for each port anywhere in the I/O bus address range of 100 to 3F8 (hex) by means of four sets of DIP switches on the cards. Interrupt levels from IRQ2 through IRQ15 (except IRQ 8, 9, and 13) are selectable by means of jumpers on the cards and interrupts are shared. An on-board Interrupt Status Register is included for use when interrupts are shared.

The cards contain a crystal-controlled oscillator and provide precise selection of baud rate from 300 to 115.2k baud. Higher baud rates are optionally possible. If you require baud rates higher than 115.2k baud, give us a call. We may be able to offer what you need at little or no extra cost.

Automatic and Request-to-Send Transceiver Control

Half- and full-duplex communications requires that the transmitter driver be enabled and disabled as needed, particularly in the RS-485 mode where communications lines are shared. These cards have two methods of controlling the driver: automatic (AUTO) for Windows applications and request-to-send (RTS) control. Under AUTO control, the UART is normally in the receive mode. When data is ready to be transmitted, the driver is enabled. The driver remains enabled for the transmission time of one character after data transfer is complete and then the card reverts to receive mode. This AUTO mode allows use of standard Windows RS-232 serial communication drivers in your application.


  • High-speed crystal oscillators to achieve higher baud rates.




Drivers and Downloads

Full list of available Downloads: Software Packages, Drivers, Manuals, and other documents

Information about our Free Software packages:

ACCES is proud to provide a full suite of software support with every Data Acquisition product. We are committed to supporting the most popular operating systems and platforms for our customers. Currently we are actively supporting XP -> 10, both 32 & 64 bit, including “Server 2008,” “Embedded,” and “Compact” flavors for all plug-and-play products including PCI, PCI Express, USB, and more. Many products continue to ship with support for additional operating systems such as DOS, Windows 95, 98, Me, NT4, and 2000.


Among the software we deliver with our products are sample programs in a wide variety of programming languages. These samples are used to demonstrate the software interfaces to our products — and many can be used as-is in your production environments, or to test functionality of the devices out-of-the-box. We’re currently actively supporting sample programs in Microsoft Visual C#, Visual Basic, Delphi, and Visual C/C++, with many devices including samples in Borland C/C++ 3.1 for DOS. Additionally we provide National Instruments LabVIEW compatible DLLs and many demonstration VIs for our devices.


Drivers for various operating systems are also provided, including active support for Windows XP -> 10 — all in both 32-bit and 64-bit flavors, and including consumer, server, and embedded varieties — as well as the 2.6 and newer Linux kernels and recent OSX / macOS versions. Many products continue to ship with driver support for Windows 95, 98, Me, NT4, and Windows 2000, but support for these operating systems is considered deprecated.

Setup Programs and Utilites

Our Data Acquisition devices also include a graphical setup utility that walks you through the process of configuring any option jumpers or switches on the device, as well as explaining a little about the various connectors present.

Many devices also include utility programs – little tools to make your use of the device easier, such as EWriter, a program that allows you to read and write data in the user-accessible EEPROM locations on all our USB data acquisitition products; or WinRISC, a “Really Incredibly Simple Communications” terminal program that lets you get started instantly with serial devices.

“Register Level” Documentation

Besides all this software in all these languages and operating systems ACCES has a policy of open and transparent development: none of our lowest-level “register” interfaces are hidden from you — we document every register in every bus card, every command in every serial board, and every usb control transfer in every USB Data Acquisition board. These lowest-level interfaces allow you to develop for our products in ANY operating system or language, regardless of our actively supporting it or having a driver for it. We have customers actively developing in ADA, Android, Python, Java, MATLAB, Solaris, and more, just by referring to our complete low-level interface documentation! And we provide the full source code to all of our drivers, regardless of operating system, to give you an even bigger head start in your own development tasks.

No Fees or Royalties

All of this software is provided at no additional charge, and is licensed under any of a variety of flexible — and royalty free — options. Check out our software license explanation if you’d like more information.

Custom Software

ACCES also offers Custom Software Services for our products. Our prices are unbelievably low, often as inexpensive as free! If you need something tweaked to support your needs, or an entire enterprise application developed from scratch, it is definitely worth your time to inquire with us, first.

Further information about available ACCES Software:

Redistributing Windows Drivers
A list of ACCES drivers and the files that compose them under different versions of Windows, so you can easily redistribute ACCES cards and drivers.

Note: only one serial port shown

Communications Interface

  • RS-485 Drive: A total of 32 transmitters and receivers allowed on one line.
  • Receiver Input Sensitivity: ±200 mV, differential input.
  • Input Common Mode Voltage: -7V to +12V.
  • Transmitter Output Drive Capability: 60 mA (100 mA short-circuit current capability). RS-485 model can drive 32-node, multidrop, two-wire twisted pair cable up to 4000 feet long.
  • Serial Data Rates: 300 to 115,200 baud, asynchronous.
  • I/O Bus Address (each port): DIP switch selectable within 100 to 3F8 (hex) range of AT bus addresses.
  • Interrupts (each port): Jumper selectable, IRQ2-7, 10-12, 14, 15.


  • Operating Temperature Range: 0° to +60°C
  • Storage Temperature Range: -50°C to +120°C.
  • Humidity: 5% to 95%, non-condensing

Power Required

  • +5 VDC at 250 mA typical, 500 mA maximum.


  • Although designed for any AT slot, if installed in an XT-style slot then IRQ10-15 will be unavailable to the card.

Regulatory Compliance

  • This product is in full compliance with CE requirements.
ModelDescriptionPrice (USD)

ISA 4 port RS-485 card, bracketed DB9’s


ISA 4 port RS-422 card, bracketed DB9’s


ISA 4 port RS-422 card, cabled DB9’s


ISA 4 port RS-485 card, cabled DB9’s