Applied Motion STAC6-C - Manual (Page 12)

12
STAC6 Hardware manual 920-0029 Rev. C
5/2/2012
Connecting to the PC using RS-485
RS-485 allows you to connect more than one drive to a single host PC, PLC, HMI or other computer. It
also allows the communication cable to be long (more than 1000 feet). But the device to which you connect
must have an RS-422 or RS-485 port.
Pin diagram is shown to the right. Wiring diagrams can be found on this and the next
page. We recommend the use of Category 5 cable. It is widely used for computer net-
works, it is inexpensive, easy to get and certified for quality and data integrity.
The STAC6 drives can be used with either two wire or four wire RS-485 implementations. The connection
can be point to point (i.e. one drive and one host) or a multi-drop network (one host and up to 32 drives).
Four wire systems utilize separate transmit and receive wires. One pair of wires must connect the host
computer’s transmit signals to each drive’s RX+ and RX- terminals. Another pair connects the TX+ and TX-
drive terminals to the host computer’s receive signals. A logic ground terminal is provided on each drive
and can be used to keep all drives at the same ground potential. This terminal connects internally to the DC
power supply return (V-), so if all the drives on the RS-485 network are powered from the same supply it is
not necessary to connect the logic grounds. You should still connect one drive’s GND terminal to
the host computer ground.
Four wire systems are better than two wire types because the host can send and receive data at the same
time, increasing system throughput. Furthermore, the host never needs to disable its transmitter, which
simplifies your software. We recommend that a 120 ohm terminating resistor be connected between RX+
and RX- at the farthest drive from the host.
+RX- +TX- GND +RX- +TX- GND +RX- +TX- GND
to PC TX+
to PC TX-
to PC RX+
to PC RX-
to PC GND
Drive #1 Drive #2 Drive #3
120
Two wire systems transmit and receive on the same pair of wires. The host must not only disable its
transmitter before it can receive data, it must do so quickly, before a drive begins to answer a query. The
RX+
RX –
TX –
TX+
GND
RS-485/422