Delta RMC101 - Manual (Page 489)

Serial (RS-232/422/485) 5.5
Communications 5-239
the RMC SERIAL offers three drivers: RS-232, RS-422/RS-485 (4-wire), and RS-485 (2-wire).
Each of the above features is described below:
• Duplex (Full or Half): Full-duplex means that each device on a serial network can send and
receive at the same time, effectively doubling the bandwidth of the network. Half-duplex means
that only one device on the network can send data at one time. For the above drivers, full-
duplex requires separate send and receive wires.
• Differential: Differential wiring uses two wires per signal which allows common mode noise
rejection. RS-232 does not use differential wiring, but instead has one wire per signal plus a
ground. Differential wiring allows for longer cable distances and greater noise immunity.
• Topology: Topology describes the layout of the network. Point-to-point means that exactly two
devices are wired together. Multi-drop means that two or more devices are chained together.
Notice that "multi-drop" with only two devices becomes point-to-point. See Serial Network
Topologies for details.
• Wires: This item refers to how many wires need to be connected between nodes. Notice that 2-
wire and 4-wire RS-485 actually requires three and five wires respectively because of the
Common in addition to the differential signal wires. See RS-232 Wiring for the RMC SERIAL
and RS-422/485 Wiring for the RMC SERIAL for details.
• Max Length: The maximum cable lengths vary depending on the baud rate, termination (for RS-
422/485), and capacitance of the cable. See RS-232 Wiring for the RMC SERIAL and RS-
422/485 Wiring for the RMC SERIAL for details.
• Flow Control: Flow control can be used with RS-232 to ensure that one device does not
overrun the other device. That is, if one device is sending data and the receiving device's
buffers get full, then it can use flow control to pause the first device's sending until it has room in
its buffers.
5.5.2.4 Serial Network Topologies
The RMC SERIAL supports two network topologies: point-to-point and multi-drop. Which
topologies are available depend on the line driver (RS-232, RS-422, or RS-485) used. See Line
Drivers: RS-232/422/485 for details on choosing the appropriate line driver.
Point-to-Point
Point-to-point means that exactly two devices are wired together. For the RMC, this means that
there will be one RMC wired to one host. All three line drivers support point-to-point, as shown
below: