Acces PCI-ICM422/2 User Manual
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Contents
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Page 1-1Manual MPCI-ICM4S.F1bChapter 1: IntroductionThese cards provide effective asynchronous serial communications in RS422 and RS485 networkson long communications lines in noisy environments. The cards feature independent serial ports anduse type 16550 buffered UARTs. The data lines are opto-isolated from the computer and from eachother to assure communication through large common mode noise.Both the RS422 and RS485 cards are 12.283 inches (312 mm) long and may be installed in 5-voltPCI-bus slots of IBM PC or compatible computers. For Windows compatibility, the cards featureautomatic control in the RS485 mode to transparently enable/disable the transmission drivers.RS422 Balanced Mode OperationThe PCI-ICM422/2 and PCI-ICM422/4 support RS422 communications and use differentialbalanced drivers for long cables and high noise immunity. These cards also have the capability toadd load resistors to terminate the communications lines. RS422 communications requires that atransmitter supply a bias voltage to ensure a known "zero" state. Also, receiver inputs at each endof the network should be terminated to eliminate "ringing". These cards support biasing by defaultand support termination by jumpers on the card. If your application requires the transmitter to beun-biased, please contact the factory.RS485 Balanced Mode OperationThe PCI-ICM485/2 and PCI-ICM485/4 support RS485 communications and also use differentialbalanced drivers for long range and high noise immunity. RS485 operation involves switchabletransceivers and the ability to support multiple devices on a single "party line". The RS485specification defines a maximum of 32 devices on a single line. The number of devices served ona single line can be expanded by use of "repeaters".PCI-ICM485/2 and PCI-ICM485/4 also have the capability to add load resistors to properly terminatethe communications lines. Receiver inputs at each end of the network should be terminated toeliminate 'ringing". Also, RS485 communications requires that one transmitter supply a bias voltageto ensure a known "zero" state when all transmitters are off. These cards support biasing by defaultand support termination by jumpers on the card. If your application requires the transmitter to beun-biased, please contact the factory.COM Port CompatibilityType 16550 UARTs are used as the Asynchronous Communication Element (ACE). These includea 16-byte transmit/receive buffer to protect against lost data in multitasking operating systems, whilemaintaining 100 percent compatibility with the original IBM serial port. |
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