Available from Interworld Electronics, Acces I/O’s PCI-422/485-2 provides two ports of either RS-422 or RS-485 per PCI slot. This half sized board was designed for either rugged embedded PC’s or high reliability standard PCs where larger boards will not fit. It comes in either isolated or non-isolated versions. The isolated version provides protection to the delicate PC components that could be damaged from induced voltages over the long serial lines. Rugged components provide an extremely long life in industrial environments.
The PCI-422/485-2 supports both RS-422 and RS-485 communications. It also utilizes differential balanced drivers for long range and noise immunity. On the isolated version, the data lines are opto-isolated from the computer and from each other to ensure communication when large common mode noise is present. In RS422 mode the PCI-422/485-2 has the capability to jumper in load resistors, which terminate the communication lines. RS-422 communications requires that a transmitter supply bias voltage to ensure a known "zero" state. Receiver inputs at each end of the network can be terminated to eliminate “ringing”. All cards support biasing by default and support termination by jumpers on the card.
In RS-485 communications, the driver must be enabled and disabled as needed, allowing all cards to share a two-wire cable. This is automatically controlled in the PCI-422/485-2. Commonly called Automated RTS, 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. This makes the PCI-422/485-2 and PCI-422/485-2I ideal for Windows 95/98/NT/2000/ME operation under RS-485.
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