Newport New Focus Picomotor 8743-CL, User Manual

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5.5 RS-485 Communication
RS-485 interface can be used to communicate with up to 31 Picomotor controllers (8743-
CL or 8743-CL) that are daisy-chained, using a single USB/Ethernet connection.
Once the desired controllers are daisy-chained using the RS-485 link cable, any one of
these controllers can be connected to a host PC via USB or Ethernet interface. The
controller on the network that is directly connected to a host PC is referred to as the
“master controller”. This controller is responsible for receiving commands from the host
PC, and sending responses, if any, back to the host PC.
NOTE: There can be only one designated master controller on the RS-485 local area
network (LAN).
All the controllers connected to a master controller via RS-485 link cable are referred to as
the “slave controllers”. There can be up to 30 slave controllers connected to 1 designated
master controller.
When the master controller receives a command from a host PC, it first determines if the
command is addressed to it or if the command is addressed to one of the slave controllers.
If the command is addressed to it, it processes the command and sends any responses back
to the host PC. On the other hand, if the command is addressed to one of the slave
controllers, it transmits the command on the RS-485 LAN. Since the controller RS-485 is
configured in a multidrop, parallel bus topology, all the slave controllers receive the
command transmitted by the master controller. Each slave controller then determines if
the command is addressed to it, and processes the same if it is the intended recipient. All
other slave controllers ignore the received command. If the command is a query (i.e.,
requires response), the slave controller that processed the command may transmit the
response on the RS-485 LAN. Once again, all the controllers on the RS-485 LAN,
including the master controller, receive the response transmitted by the slave controller.
The master controller determines that the information it received on the network was a
response to a command it had initially transmitted on the network, and sends this response
to host PC; all the slave controllers ignore the response they received.