PCI-COM485-4 Four Port RS485

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  • Universal PCI, PCI-X, 3.3V and 5V compatible (Call for PCI-Express availability)
  • Four-port serial communications card for PCI bus
  • Supports RS-485 multidrop networks
  • Includes type 16550 UART with 16-byte FIFO buffers
  • Baud rates up to 460,800 baud
  • Automatic control of RS-485 driver under Windows systems
  • Choice of I/O connection methods
  • No base address or IRQ switches to set
  • Support for Wind River VxWorks (call for ordering information)
  • Designed, made, supported, and manufactured in the USA
Last updated on November 2, 2023, 6:26 pm


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PCI Four-Port RS-485 Serial Cards

The PCI-COM485-4 is a four-port, asynchronous serial communications card designed for use in PCI-Bus systems. The cards feature four independent, asynchronous RS-485 serial ports, type 16550 buffered UARTs, and for Windows compatibility, automatic control to transparently enable/disable the transmission drivers. The card may be installed in any 3.3V or 5V PCI or PCI-X slot.

There are two I/O Connector options. Model PCI-COM485-4 includes a single 25-pin connector on the mounting bracket plus a “spider” or breakout cable that terminates in four 9-pin D-type male connectors. Thus, this version only requires one I/O slot. The standard model PCI-COM485-4 S1 includes two 9-pin male connectors on the card mounting bracket plus a second mounting bracket with two more 9-pin male connectors plus ribbon cables to connect them to the headers on the card.

Each independent port supports RS-485 balanced mode transmission/reception. Each port has the capability to add bias voltage. (RS-485 communication requires that one transmitter in the network must supply a bias voltage to ensure a known “zero” state when all transmitters are OFF.) Also, receiver networks at each end of the networks should be terminated to eliminate ringing. These cards support that need by means of jumpers on the card.

Type 16550 UARTs are used as the asynchronous communication elements. These include a 16-byte transmit/receive FIFO buffer to protect against lost data in multitasking systems while maintaining 100% compatibility with the original IBM port.

A crystal oscillator is located on the card and permits precise baud rate capability up to 115,200. Higher baud rates, up to 460,800 baud, are achieved by changing a jumper on the card. The driver/receiver used, type 75176, is capable of driving extremely long communications lines at high baud rates. They can drive up to +/- 60 mA on balanced lines and receive inputs as low as 200 mV differential signal superimposed on common mode noise of +12V to -7V. In case of communication conflict, the driver/receivers feature thermal shutdown. PCI-COM485-4 supports Half-Duplex communications with two-wire cable connections. Half-Duplex allows traffic to travel in both directions, but only one way at a time.

When the card is first installed, Windows will detect it as new hardware and assign it an IRQ number and base address. There are no switches to set or base addresses to assign, making it easy to use. From this point on, the card behaves as standard COM ports at COM 5,6,7, and 8. You cannot set or change the card’s base address, you can only determine what the system has assigned. The PCI Bus supports 64K of I/O address space so your card’s address may be located anywhere in the 0000 to FFFF range.


In RS-485 communications, the driver must be enabled and disabled as needed, allowing all cards to share a two wire cable. The PCI-COM485-4 controls the driver automatically. With automatic control, the driver is enabled when data is ready to be transmitted. The driver remains enabled for one additional character’s transmission time after data transfer is complete and then is disabled. The receiver is also normally enabled, then disabled during RS-485 transmissions, and then re-enabled after transmission is completed (plus one character transmission time). The PCI-COM485-4 automatically adjusts its timing to the baud rate of the data.




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.

Communications Interface

  • I/O Connection: 9-pin D-sub connectors.
  • Serial Ports: Four shielded male D-sub 9-pin IBM AT style connectors compatible with RS-485 specifications. (Note: On model COM485-4, the breakout cable terminates with four female D-sub 9-pin connectors.)
  • Character length: 5, 6, 7, or 8 bits.
  • Parity: Even, odd or none.
  • Stop Interval: 1, 1.5, or 2 bits.
  • Serial Data Rates: Up to 115,200 baud, Asynchronous, A faster range of rates, up to 460,800, is achieved by jumper selection on the card. Type 16550 buffered UART.
  • Address: Continuously mappable within 000 to FFFF (hex) range of PCI bus addresses.
  • Receiver Input Sensitivity: ±200 mV, differential input.
  • Common Mode Rejection: +12V to -7V
  • Transmitter Output Drive Capability: 60 mA, with thermal shutdown.


  • Operating Temperature Range: 0 o to +60 o C
  • Storage temperature Range: -50 o to +120 o C
  • Humidity: 5% to 90%, non-condensing.
  • Power Required: +5VDC at 125 mA typical, -12VDC at 5 mA typical, +12VDC at 5 mA typical, 750 mW total power consumption.
  • Size: 7.82″ (198 mm) long by 3 7/8″ (99 mm)

Regulatory Compliance

  • This product is in full compliance with CE requirements.
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