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pcl-746 image

4-port RS-232/RS-422/RS-485 Interface Card


Programming Example
Ordering Information


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The PCL-746 is a four port serial communication interface card. The main feature of this card is that each port can be configured individually to either RS-232, RS-422, or RS-485 using on-board jumpers. The card uses 16C550 UARTs and improved interrupt handling for reliable operation at transmission speeds of up to 115 Kbps.

The card's 16C550 UARTs have on-chip 16-byte FIFO buffers. The UARTs buffer data into 16-byte packets before putting it on the bus. This drastically reduces CPU load and avoids data loss when the system is busy and cannot process the interrupt quickly. These FIFO buffers make the card especially suitable for high speed serial I/O under Windows.

This PCL-746 supports two operation modes: standard mode and enhanced mode. In standard mode all four ports act as normal PC serial communication ports (COM1, COM2, COM3, and COM4) with normal default addresses and IRQs. In enhanced mode all four ports can be set to share the same IRQ. When an on-board interrupt occurs, the interrupt status register indicates which port has generated it. The shared interrupt can be set to most common (extended) AT interrupts. This simplifies programming, speeds up interrupt processing, and frees up interrupts for other devices.

The PCL-746 comes with the PC-ComLIB communication software package, consisting of a configurable DOS driver and a programming library that supports most common languages. The RS-485 mode automatically senses the direction of incoming data and switches its transmission direction accordingly. This feature means your network looks and acts just like an RS-232 network. Application software written for half duplex RS-232 can be used without modification. Moreover, you can simply and quickly build an RS-485 network with just two wires.



  • Interface to PLC, barcode reader, scale, POS
  • Interface to modem, mouse, plotter, printer, BBS
  • RS-232 terminal interfaces
  • Multidrop communication networks
  • Long-distance serial links
  • Multi-user operating systems
  • Laboratory data collection and process control



  • Four independent RS-232, RS-422, or RS-485 serial ports
  • Each port is individually configurable with on-board jumpers
  • Speeds up to 115 Kbps
  • 16C550 UARTs with 16-byte FIFO
  • Complete RS-232 modem-control signals
  • Use up to two cards for a total of eight ports in one system
  • Interrupts (jumper selectable): 3, 4, 5, 7, 9, 10, 11, 12 or 15
  • On-board interrupt status register for greater throughput
  • RS-232/RS-422/RS-485 modes (jumper selectable)
  • Automatic data flow control in RS-485 mode
  • Supports 2 wire or 4 wire RS-422/RS-485 operation
  • Space reserved for optional surge protection on all port lines (in RS-422/RS-485 mode)
  • Space reserved for termination resistors
  • LED indicators on each port indicate data flow
  • Compatible with PC-standard ports: COM1 to COM4
  • Compatible with Arnet 4-port cards supporting SCO UNIX/XENIX
  • PC-ComLIB software included


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  • Number of ports: 4
  • Protocol selection: RS-232, RS-422 or RS-485 (jumper selectable)
  • UART: 4 x 16C550 16-byte FIFO
  • Base I/O address selection: 100H to 3C0H
  • Interrupt status address selection: 000H to 3F0H
  • IRQ selection: 3, 4, 5, 7, 9, 10, 11, 12 or 15
  • Data bits: 5, 6, 7, 8
  • Stop bits: 1, 1.5, 2
  • Parity: Even, odd or none
  • Power consumption: 5V@800mA typical, 1.5A max., /-12V@60mA typical, 120mA max
  • Operating temperature: 32 to 122 degF (0 to 50 degC)
  • Cables: 30-cm male DB-37 to four male DB-25 cable
  • Dimensions: 185 mm x 100 mm
  • Weight: 1.1 Kg (including cable)

    RS-232 Interface
  • Signals: TxD, RxD, RTS, CTS, DTR, DSR, DCD, RI, GND
  • Mode: Asynchronous full duplex, point-to-point
  • Transmission speed: 115 Kbps max.
  • Max transmission distance: 50 feet (15.2 meters)
    RS-422 Interface
  • Signals: TxD , TxD-, RxD , RxD-, RTS , RTS-, CTS , CTS-, GND
  • Mode: Asynchronous full duplex, point-to-point
  • Transmission speed: 115 Kbps max.
  • Max transmission distance: 4000 feet (1220 meters)
    RS-485 Interface
  • Signals: DATA , DATA-, GND
  • Mode: Half duplex, multidrop
  • Transmission speed: 115 Kbps max.
  • Max transmission distance: 4000 feet (1220 meters)
    Programming Library (PC-ComLIB)
  • Optimized, small size resident (TSR) interrupt driver
  • Supports C, BASIC, Pascal, Clipper, and assembly
  • Includes DataScope data viewer, terminal emulator, and self-diagnostic utilities for easy troubleshooting/debugging

Programming Example Return to top of page

The following C program shows a simple data transfer test. It uses a PC-ComLIB function call to send data between Port 1 and Port 2 at a rate of 57.6 Kbps

/* Execute the PC-ComLIB TSR driver first*/




        /* Setup Port 1 and Port 2; baud = 57600; 

            data = 8 stop = 1 no parity */



        /* Enable communication ports */



        /* Transmit data on Port 1 */

        sio_write(1," Hello ",7);


        /* Receive data on Port 2, store in buf1*/


        /* Print received data */


        /* Disable communication ports */




Ordering Information

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PCL-746 4-port Serial Interface Card. Includes 30-cm DB-37-to-DB-25 cable, PCLS-802 PC-ComLIB software.
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USA Office

Address: 1480 Gulf Road, Suite 837,
PO Box 1364
Point Roberts, WA 98281

Western Canada - Vancouver BC

Tel:1.800.663.6001 or 1.604.925.6150
Address: 2454 Haywood Ave
West Vancouver, BC V7V 1Y1

Eastern Canada - Markham, Ontario

Tel:1.800.465.0164 or 1.905.513.7027