48 Computer Interfacing
Picomotor Controller RS-485 LAN Topology
Note that a multidrop bus is a computer bus in which all components are connected
to the same set of electrical wires. A process of arbitration determines which device
gets the right to be the sender of information at any point in time. The other devices
must listen for the data that is intended to be received by them. Multidrop buses
have the advantage of simplicity and extensibility.
5.5.1 Setting up an RS-485 Network
All the controllers on an RS-485 network must have unique addresses in order for a
host PC to communicate with them individually. In the case of Picomotor
Controllers, these addresses can be values (integers) between 1 and 31. Since the
default address of a controller is 1, users must change the addresses of the
controllers to unique values.
There are two (2) ways—manual and automatic—in which unique addresses can be
assigned to all the controllers. The manual approach involves powering ON only
one controller at a time, connecting this controller directly to a host PC via
USB/Ethernet, changing the address to a desired value using “SA” command, saving
the address in the controller using “SM” command, and powering OFF the
controller. This process must be repeated for all the controllers on the network.
Picomotor Controllers support a novel automatic approach that allows a master
controller to assign unique addresses to all the slave controllers. The automatic
approach involves powering ON all the controllers on the network, issuing “SC”
command to initiate scan process, and waiting for the scan process to complete by
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