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© Sealevel Systems, Inc.
7101 Manual | SL9160 9/2021
APPENDIX C - ELECTRICAL INTERFACE, CONTINUED
RS-485
RS-485 is backwardly compatible with RS-422; however, it is optimized for party line or multi-drop
applications. The output of the RS-422/485 driver is capable of being Active (enabled) or Tri-
State (disabled). This capability allows multiple ports to be connected in a multi-drop bus and selectively
polled. RS-485 allows cable lengths up to 4000 feet and data rates up to 10 Megabits per second. 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. This interface is ideal for multi-drop or
network environments. RS-485 tri-state driver (not dual-state) will allow the electrical presence of the driver
to be removed from the line. Only one driver may be active at a time and the other driver(s) must be tri-
stated. RS-485 can be cabled in two ways, two wire and four wire mode. Two wire mode does not allow for
full duplex communication and requires that data be transferred in only one direction at a time. For half-
duplex operation, the two transmit pins should be connected to the two receive pins (Tx+ to Rx+ and Tx- to
Rx-). Four wire mode allows full duplex data transfers. RS-485 does not define a connector pin-out or a set
of modem control signals. RS-485 does not define a physical connector.
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 Sealevel Systems adapter is a DTE interface.