STAC6 Drives and Microstepping Motors:
User Manual
(Discontinued Product)
• 1.7 •
1:
H A R D W A R E
RS 485 and RS 422 Communications
CONNECTING TO THE PC USING RS-485
RS-485/422 allows connection of more than one drive to a single
host PC, PLC or other computer. It also accommodates a longer
cable (more than 1000 feet) for devices that have a RS-485/422 port.
A SHORT TUTORIAL ON RS-485 & RS-422
RS-485 in the strictest definition is a "2-wire" interface that
allows multi-node connections limited to "Half-duplex" serial
communications. Up to 32 nodes that both transmit and receive
can be connected to the network. RS-422 in the strictest definition
is a "4-wire" point-to-point connection that allows "Full-duplex"
serial communications when connected to a single node. RS-422
has one node that is the driver or transmitter and up to 10 nodes
that are receivers. RS-422 was not designed for a true multi-node
network.
2- wire interfaces require a network node, master or slave, must be
able to tristate its transmitter to allow other nodes to use the
network when required. For high speed baud rates this must be
done very quickly to avoid communications collisions.
4-wire interfaces can go beyond the simple point-to-point and
accommodate multi-node networks if the slave node is capable of
tri-stating their transmitters as required in the 2-wire networks.
Some RS-485 devices are setup to do this and can be used in a
4-wire configuration.
On the AMP Servo drives, the RS-485 can be implemented
with either "2-wire" or "4-wire" interfaces. In both cases,
communications are still limited to "Half-duplex" because of
the nature of the serial communications protocols used. 4-wire
implementations can sometimes be easier due to the greater
number of Host RS-232 to RS-485 adapters that support the 4-wire
interface. 2-wire implementations may require special Host adapters
that support
