The Technisys RS422 1 of 2 Select Chassis is a fully integrated device designed to allow 1 of 2 RS422 inputs to be selected by RS232 control or a local manual override. It is housed in a 1U rack mount enclosure and includes an auto-ranging power supply for use internationally.
I/O is through D15F connectors. A three position, locking toggle switch (SELECT) is located on the front panel to provide the ability to select either INPUT A or B for output. Front panel LEDs indicate which input has been selected. In this manual mode, the processor is by-passed and control is implemented directly from the front panel switch.
When the front panel SELECT switch is placed in REMOTE position, the appropriate LED illuminates and input selection is controlled by a command sequence from either of the two independent RS232 serial ports through DB25F connectors. There is an input buffer for each serial port so characters are continually received from either serial port or both. Input counters and timers prevent problems from a jabbering serial port.
On power failure, the unit defaults to INPUT A through normally closed (NC) relays. These relays are held open during normal operation so that true RS422 receivers and drivers can be employed to receive and transmit active RS422 signals. When power is off or has failed, the relays return to their NC position and signals will pass through without being buffered.