Black Box IC171C - Manual (Page 9)

4
RS422/485 SERIAL INTERFACE PLUS
RS-530 and RS-449
RS-530 and RS-449 (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 backward-compatible
and is replacing RS-449. RS-530 is defined on a 25-pin D sub-connector.
Figure 2-1. RS-422/530 Connection.
RS-485
This interface is very similar to RS-422 is several ways. RS-485 is a differential
interface that allows cable lengths up to 5000 feet (1524 m) and data rates up
to 10 Mbps. The signal levels for RS-485 are the same as those defined by RS-
422. RS-485 has electrical characteristics that allow for
32 drivers and 32 receivers to be connected to one line.
TX+
TX-
RX+
RX- RX+
RX-
TX+
TX-