Chapter 1: Installation
Manual Number: 000750-006-5
Page 15
Appendix B: Electrical Interface
RS-422
The RS-422 specification defines the electrical characteristics of balanced voltage digital interface
circuits. RS-422, unlike RS-232, is a differential interface that defines voltage levels and driver/
receiver electrical specifications. On a differential interface, logic levels are defined by the difference
in voltage between a pair of outputs or inputs. In contrast, a single ended interface, for example
RS-232, defines the logic levels as the difference in voltage between a single signal and a common
ground connection. Differential interfaces are typically more immune to noise or voltage spikes that
may occur on the communication lines. Differential interfaces also have greater drive capabilities
that allow for longer cable lengths. RS-422 is rated up to 10 Megabits per second and can have
cabling 4000 feet long. RS-422 also defines driver and receiver electrical characteristics that will
allow 1 driver and up to 32 receivers on the line at once. RS-422 signal levels range from 0 to +5
volts. RS-422 does not define a physical connector.
RS-530 and RS-449
RS-530 and RS-449 (a.k.a. EIA-530 and EIA-449) are similar to RS-422 and RS-485 in the fact
that they are differential interfaces, but these two standards provide a specified pin-out that defines
a full set of modem control signals that can be used for regulating flow control and line status.
RS-449 is defined on a standard 37 pin D sub connector while RS-530 is backwardly compatible and
is replacing RS-449. RS-530 is defined on a 25 pin D sub connector.
RS-530 (a.k.a. EIA-530) compatibility means that RS-422 signal levels are met, and the pin-out for
the DB-25 connector is specified. The EIA (Electronic Industry Association) created the RS-530
specification to detail the pin-out, and define a full set of modem control signals that can be used for
regulating flow control and line status. The RS-530 specification defines two types of interface
circuits, Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE). The
adapter is a DTE interface.
TX+
TX-
RX+
RX-
RX+
RX-
TX+
TX-
Figure 10: RS-422/530 Example
