Rs485 Cable; Rs485 One Talker - Many Listeners, Half Duplex - Brainboxes CC-310 Hardware Manual

PCI VELOCITY / OPTO ISO RS422/485

RS485 Cable.

For best noise immunity use twisted pair cables to make the
RS485 connection. In Half Duplex wiring only 1 twisted cable pair
is needed. Two twisted pair cables are needed for Full Duplex
communications.
Use screened twisted pair Belden cable 9729 and 9829, UL
type 2493 and 2919 or IBM Part No 4716748 cable to make the
RS485 connection. Terminate the twisted pair cable at either end in
its characteristic impedance, which for the Belden 9729 cable is
120 Ohms. Unscreened Belden type 8795 may also be used in less
noisy environments.

RS485 One Talker - Many Listeners, Half Duplex.

There are several schemes for connecting RS485 devices
depending on the characteristics of the system. In many cases there
will be only one device, which can transmit, data and all the others
simply listen to it. This scheme is used for theatrical lighting
intensity control in the DMX512 standard. This is shown in Figure
4-2, below. For the talker the RS485 TXD GATE jumper should
remain in the factory set position, i.e. transmitter is always enabled.
There is NO multiplexing of the TXD and RXD lines. Data is only
flowing one way, from PC outwards, and is thus a Half-Duplex
configuration, only one twisted pair cable is needed.
Figure 4-2. RS485 1 Talker Many Listeners.
Note: The Receiver end of MAIN line terminated in
characteristic impedance by ONBOARD resistor networks, stubs
RS422/485 Information
Chapter 4 Page 45