Research Concepts RC2000C - Manual (Page 84)

76 RC2000C Az/El Tracking Antenna Controller Appendix E Communications Protocol
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Appendix D - The RCI RS422 Interface Specification
Introduction
The purpose of this document is to explain the key parameters needed by a user to interface to the RCI
RS422 Interface. This interface is compatible with the SAbus and can be readily integrated into an
existing SAbus network. A few query and control commands are all that are needed to control the
equipment and fetch all data from it. The user should refer to RCI document ‘Communications Protocol’
for the specific program commands and descriptions of their functions.
Electrical Specifications
RS-422 is a unipolar, balanced 5-volt serial interface designed to connect equipment which must
exchange data over considerable distances with high-noise immunity and high speed. Standard IC
drivers and receivers are available for RS-422 that convert to and from TTL logic levels. The RS-422
drivers/receivers in the controllers allow up to 32 devices to be connected in parallel with up to 1,500
feet between the master and group of controllers.
Physical Specifications
The physical implementation of the interface takes the form of a 9-pin "D" connector located on the rear
panel of the controller. This connector and its wiring is compatible with EIA RS-449, which is the
mechanical specification for RS-422/423-compatible equipment. The 9-pin connector chosen is
described as the secondary interface in RS-449 and has only the four data lines and shield. No
hardware handshaking is used in the protocol, so all the control lines specified for the standard 37-pin
connector are not needed. The controller operates as a slave only and has a female connector,
whereas master devices have male connectors. Multiple controllers, connected in a daisy chain
fashion, can operate in electrical parallel with only a single 5-conductor cable required to connect all
devices controlled by a master. Figure 1 illustrates the connection of a master and multiple controllers.
RS-422 Protocol
The interface is a multi-drop, balanced line, asynchronous, full-duplex communications link designed to
interconnect equipment for remote control and switching applications. Products that are compatible can
be linked together over a parallel-connected 4-wire circuit without regard to their particular function.