Envision Peripherals NV3128 - Manual (Page 65)

NV3128 RS-422A Machine-Control Data Routing Switch 4-3
CHAPTER FOUR - THEORY OF OPERATION
4.1 SYSTEM
Fig 1.5 is repeated here to demonstrate the bidirectional flow of data through
the routing switch. The illustration shows a controlling machine sending and
receiving data through a controlled port on the router. Two crosspoints enable
the forward and reverse data paths through the switch. A controlled machine
receives and answers this command traffic through a controlling port.
4.1.1 CONTROL STRUCTURE
The Universal Control/Command Interpreter module receives commands
from an external control system and uses that information to pre-set an address
map of the entire crosspoint matrix. The address map is stored in double-
buffered RAM to prevent command updates from interfering with any take
activity in process. A programmable gate array transforms the address map into
the addresses and control commands that govern the operation of the crosspoint
modules. The mapping activity is continuous, with the Universal Control/
Command Interpreter module constantly pre-loading the crosspoint’s double-
buffered registers. At the take interval, a strobe pulse derived from the
reference input on the Universal Control/Command Interpreter module updates
the crosspoint registers with the pre-set information.
The Universal Control/Command Interpreter module additionally sends
information based on incoming commands to the I/O modules' on-board port
controllers. This data effectively causes one port to be configured as controlled,
and the other port in the route to be configured as controlling. The controlling
port will be associated with the source or destination parameter, depending on
the configuration of Reverse Src/Dest. See the explanation of Reverse Src/Dest
in the UniDiag manual for details.