Envision Peripherals manual Architecture Background, NV3128 RS-422A Machine-Control Data Switch

For very high reliability applications, a redundant controller can also be added to the frame, with circuitry provided for automatic changeover.

With its duplex complexity, RS-422A has long been a troublesome method of plant signal routing. The NV3128 untangles the problems unique to this data type to offer an innovative, low-cost solution that merges easily into a facility’s over-all routing plan.

Ascaled-down version of the switch, with 64 of the 128 ports enabled, is available as model NV3128-64.

1.2ARCHITECTURE

BACKGROUND:

The duplex nature of RS-422A communication creates its own level of complexity. The Electronic Industry Associates RS-422A, is a balanced, serial, 4-wire transmission technique with a line driver and receiver at either end of the link. In the typical video or audio production-machine hookup, one machine is master, and one or more machines are slaved. The master is referred to as a controlling device, the slave as a controlled device. The controlling device issues commands to the controlled device via a D connector over pin pair 3/8. The controlled device receives the commands over the same pin pair, 3/8, and transmits status, acknowledgement and diagnostic data back over pin pair 2/7. The controlling device receives this feedback over pin pair 2/7. Fig. 1.1 illustrates this fundamental connection.

NV3128 RS-422A Machine-Control Data Switch 1-4