Baldor MicroFlex, Installation Manual

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Input / Output 5-15 MN1919
The RS232 port is configured as a DTE (Data Terminal Equipment) unit. Both the output and
input circuitry are single ended and operate between ±12V. The port is capable of operation at
up to 57.6 Kbaud. The maximum recommended cable length is 3m (10ft) at 57.6 Kbaud (the
factory preset rate). When using lower baud rates, longer cable lengths may be used up to
maximum of 15m (49ft) at 9600 baud.
5.4.2 Multidrop using RS485 / RS422 cable
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
MicroFlex, 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 39. 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 drive that was chosen in the Select Controller dialog in Mint WorkBench.
Master and final slave are
shown with terminating
resistors, T
R
, typical value
120 Ω .
Network slave
T
R
RX-
DGND
RX+
TX+
TX- RX-
DGND
RX+
TX+
TX-
RX-
DGND
RX+
TX+
TX-
Twisted pairs
T
R
Connect overall shield
to connector backshell.
Network slave
Network
master
Figure 39 - 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.