Envision Peripherals NV3128 - Manual (Page 69)

NV3128 RS-422A Machine-Control Data Routing Switch 4-7
4.2.4 I/O ASSEMBLY: EM0040-XX
The I/O module is a bidirectional interface between the router's
crosspoint matrix and the external machines. Two modules, each
supporting 64 ports, make up the full complement of I/O circuits. The
assembly plugs simultaneously into both backplanes, communicating
with the crosspoint module through the Signal Backplane and with the
external machines through the I/O Backplane.
A total of 64 proprietary receiver/driver submodules pass data to and
from the I/O backplane. Each submodule makes the D connector it
services function as either a controlled or a controlling device, depending
on whether it is addressed as a Source or as a Destination.
Two 64x64 crosspoint ICs use control information received from the
Command Interpreter to gate the submodule transmitters and receivers
on or off appropriate to the directions of data flow through the port.
The command information is resistor-coupled from the Signal Backplane
into line buffer/driver circuits and their associated resistor networks. A
similar circuit arrangement receives crosspoint data from the Signal
Backplane and applies it to the port submodules for transmission to
external machines.
Receive data from the port submodules is driven over the Signal
Backplane to the Crosspoint Module by drivers ICs.
Submodules each operate separately on the raw DC input voltage to
provide +5VDC operating levels for 1/2 the available circuits. By thus
dividing the circuitry, the impact block of a failure is correspondingly
reduced.