Isolated Multiprotocol (RS422/RS485)Serial Communications Card
The Model 104-ICOM-2S Serial Communications Card can be installed in a PC/104 stack and provide effective communication on long lines in noisy environments. Data lines are opto-isolated from the computer and from each other to assure communication even when large common mode voltages and noise are imposed.
By means of jumper placement on the card, each port can be setup for either RS-485 or RS-422 operation. RS-422 operation uses differential balanced line drivers for long range and high noise immunity. RS-485 operation improves on that by providing multi-drop capability for as many as 32 devices. RS-485 communication requires that one device on the network provide a bias voltage to ensure a known “zero” state when all transmitters are off. Also, receiver inputs at each end of the network should be terminated to avoid “ringing”. Both ports on the 104-ICOM-2S support those needs, bias is provided as a standard, and termination by means of jumper selection.
The card supports half-duplex and full-duplex communications in 2- and 4-wire cable connections. Half duplex allows traffic to travel in both directions, but only one way at a time. In full-duplex operation, data travels both ways at the same time. Most RS-485 communications use the half-duplex mode because only a single pair of wires needs to be used and installation costs are dramatically reduced. In RS-485 operation the driver must be enabled and disabled as needed to allow all cards to share a two wire or four wire cable. Auto-RTS control circuits on the 104-ICOM-2S enable the driver when data is to be transmitted. When transmission is complete, the driver is automatically disabled. The receiver at that port is disabled during transmission time and then enabled at the completion of data transmission.
Type 16550 UART’s are used. These include 16-byte FIFO buffers to protect against data loss in multitasking operating systems. The on-board crystal oscillator and supporting circuitry provides means for selection of standard baud rates up to 115,200. Up to 460,000 Baud can be achieved via a factory option.
Connections are made with the card’s serial ports via standard DB9 Male connectors (equipped with jack-screws to eliminate vibration worries in harsh environments and applications).
Standard 16550 compatible UART ensures compatibility with DOS, Windows XP -> 10, both 32 & 64 bit, Linux and all other major operating systems.