Envision Peripherals NV3128 - Manual (Page 14)

NV3128 RS-422A Machine-Control Data Switch 1-4
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.
A scaled-down version of the switch, with 64 of the 128 ports enabled, is
available as model NV3128-64.
1.2 ARCHITECTURE
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.