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pcl-743b, 745b image

RS-422/485 Card


Ordering Information

Notes PCL-745B

Introduction Return to top of page

The PCL-743B/745B card provides two RS-422/485 serial ports. Each port has a 16C550 UART with on-chip 16-byte FIFO buffer for reliable high speed serial I/O. The UART buffers 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, especially useful for high speed serial I/O under Windows.

The PCL-745B differs from the PCL-743B in that it utilizes on-board optical isolators to protect your PC and equipment against damage from ground loops, increasing system reliability in harsh environments.

The PCL-743B/745B includes the PC-ComLIB communication software package. The package consists of a configurable DOS driver, a programming library that supports most common languages (such as C, Pascal, Visual Basic, assembly and Clipper) and DataScope. DataScope is a data viewer and terminal emulator with self-diagnostic utilities for easy troubleshooting and debugging.

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.

Applications Return to top of page

  • PLC monitoring and control
  • Serial communication interface for harsh environments
  • Data entry terminal
  • Remote data acquisition and control systems
  • Instrument controller and distributed control systems

Features Return to top of page

  • Two independent RS-422/RS-485 serial ports
  • Provides 500 VDC isolation (PCL-745B only)
  • 16C550 UARTs with on-chip 16-byte FIFO
  • Transmission speeds up to 115 Kbps
  • I/O address and interrupt selectable
  • Wide IRQ selection: 3, 4, 5, 6, 7, 9, 10, 11, 12 or 15
  • Supports 2 wire or 4 wire operation
  • Supports Tx, Rx, RTS, and CTS signals
  • Automatic RS-485 data flow control
  • Space reserved for termination resistors
  • Space reserved for optional surge protection on data lines
  • Supports standard DOS COM1, COM2, COM3, and COM4
  • Includes PC-ComLIB software


Specifications Return to top of page

  • Number of ports: 2
  • UART: 2 x 16C550 with 16-byte FIFO
  • Signal support: TxD , TxD-, RxD , RxD-, CTS , CTS-, RTS and RTS-
  • I/O address: From 200H to 3F8H
  • IRQ: 3, 4, 5, 6, 7, 9, 10, 11, 12 or 15
  • Isolation voltage: 500 VDC (PCL-745B only)
  • Power consumption: 5V@400 mA typical, 950 mA max.
  • Connectors: Dual DB-9 male connectors
  • Operating temperature: 32 to 122 degF (0 to 50 degC)
  • Dimensions: 7.3" x 3.9" (185 mm x 100 mm)
  • Shipping weight: 1.3 lb. (0.6 Kg)

Ordering Information Return to top of page

RS-422/485 interface card. Includes PC-ComLIB software.
Isolated RS-422/485 interface card. Includes PC-ComLIB software.

Notes Return to top of page

Project: PCL-745B

Card Hardware Revision: A1

Objective: Develop a program in C using PC-COMLIB functions that will send all of the letters of the alphabet out of one port and receive the characters on the other port using a hardware loopback in (a) RS-422 mode, and (b) RS-485 mode.

Operating System: DOS 6.22

Hardware Setup:


SW1 = A4 on
SW2 = A4 and A8 on
JP1 = 2-3
JP2 = 2-3
JP3 = 5
JP4 = 7


SW1 = A4 on
SW2 = A4 and A8 on
JP1 = 1-2
JP2 = 1-2
JP3 = 5
JP4 = 7


char buf1[40];
/* Setup PORT3 & PORT4 : baud = 9600
data = 8, stop = 1, no parity */
/* Enable communications ports */
/* Set 1 second timeout */
/* Transmit Data on port 3 */
/* Receive data on Port 4, store in buffer */
/* Print received data */
/* Disable communication ports */
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