National Instruments PXI-8423/4 RS-485 Interface Module

The National Instruments PXI-8423/4 (Part Number: 777737-04) is a 4-port, RS-485 Interface Module. Because each match of differential links is a transmission line, the user should effectively end the line to keep away from reflections. A typical technique for termination of a two-wire RS-485 multipoint arrangement is comprised of introducing ending resistors at each finish of the multipoint configuration. If the user interfaces numerous instruments in a chain, then they require an ending resistor just on the first and last instrument. The ending opposition must match the trademark impedance of the transmission line (commonly 100 to 120 Ω). The user can arrange a discretionary DB-9 RS-485 end connector that contains worked in end resistors for simple end from National Instruments.

A transmission line enters an uncertain state if there are no axes that are transmitting on it. This vague state can make the beneficiaries get invalid information bits from the noise on the link. To keep a line from accepting these information bits, constrain the transmission line to a known state. To do this, introduce two 620 Ω polarization resistors on an axis in the transmission line. The result is a voltage divider that powers the voltage between the differential match to under 200 mV, the limit voltage for the receiver. The user should introduce these resistors just on one axis.

This RS-485 Interface Module has 2000 V disengagement and is compatible with a standard PC serial port, Windows 2000/NT/9x, full Windows 2000/9x Plug and Play similarity for switchless design, and interrupt sharing between ports.

PXI-8423/4 Obsolete Status has been announced by National Instruments, but the module will still be available for purchase and repairs by Apex Waves.