4-20 Input / Output
MN1957
www.baldormotion.com
The RS232 port is configured as a DCE (Data Communications Equipment) unit so it is
possible to operate the controller with any DCE or DTE (Data Terminal Equipment). Full
duplex transmission with hardware handshaking is supported. Only the TXD, RXD and
0V GND connections are required for communication, but since many devices will check the
RTS and CTS lines, these must also be connected. Pins 4 and 6 are linked on the
NextMove ESB-2. The maximum recommended cable length is 3 m (10 ft) at 57.6 Kbaud
(the factory preset rate). When using lower baud rates, longer cable lengths may be used up
to maximum of 15 m (49 ft) at 9600 baud.
4.4.8 Multidrop using RS485 / RS422
Multidrop systems allow one device to act as a ‘network master’, controlling and interacting
with the other (slave) devices on the network. The network master can be a controller such
as NextMove ESB-2, a host application such as Mint WorkBench (or other custom
application), or a programmable logic controller (PLC). RS422 may be used for multi-drop
applications as shown in Figure 24. Four-wire RS485 may be used for single point-to-point
applications involving only one Baldor controller. If firmware is updated over RS485/RS422,
it can only be downloaded to the controller that was chosen in the Select Controller dialog in
Mint WorkBench.
Figure 24: 4-wire RS422 multi-drop connections
Each transmit/receive (TX/RX) network requires a termination resistor at the final RX
connection, but intermediate devices must not be fitted with termination resistors. An
exception is where repeaters are being used which may correctly contain termination
resistors. Termination resistors are used to match the impedance of the load to the
impedance of the transmission line (cable) being used. Unmatched impedance causes the
transmitted signal to not be fully absorbed by the load. This causes a portion of the signal to
be reflected back into the transmission line as noise. If the source impedance, transmission
line impedance, and load impedance are all equal, the reflections (noise) are eliminated.
Termination resistors increase the load current and sometimes change the bias requirements
and increase the complexity of the system.
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Servo Systems Co. • 115 Main Road • P.O. Box 97 • Montville, NJ,
07045-0097 • (973) 335-1007 • Toll Free: (800) 922-1103
Fax: (973) 335-1661 • www.servosystems.com
