Appendix C - Electrical Interface
OMG-USB-485-1
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Appendix C - Electrical Interface
RS-530
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.
RS-422
The RS-422 specification defines the electrical characteristics of balanced voltage
digital interface circuits. RS-422 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.
