7705 SAR Interfaces
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Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
In a SCADA network, the 7705 SAR provides the communications infrastructure to connect
the central masters to multiple RTUs at remote locations, where the masters and RTUs
communicate over serial RS-232 or X.21 links (synchronous or asynchronous). The
7705 SAR-8 or 7705 SAR-18 located at the master site contains the Integrated Services
card, which provides the MDDB bridge functionality and acts as the MDDB master. Remote
7705 SAR nodes connected to RTUs are referred to as MDDB slaves.
For both master and slave applications, the 7705 SAR must be physically connected to the
SCADA device by one of the following:
• a 7705 SAR-8 or 7705 SAR-18 using the 12-port Serial Data Interface card (supports
both RS-232 and X.21 links)
• a 7705 SAR-H using the 4-port T1/E1 and RS-232 Combination module (supports
RS-232 links only)
• a 7705 SAR-Hc using an on-board RS-232 serial port (supports RS-232 links only)
The 12-port Serial Data Interface card also supports an RS-530/RS-422 interface with the
use of an adapter cable that connects to a DB15 connector on the front of the X.21 distribution
panel. There is no configuration specifically for the RS-530/RS-422 interface; configuration is
done in X.21 mode and applies to the RS-530/RS-422 interface when it is physically enabled
through hardware. For information about 12-port Serial Data Interface card adapter cables,
see the 7705 SAR Serial Data Interface Card Installation Guide.
Multidrop data bridge is supported only at subrate speeds (less than 64kb/s) on X.21
interfaces.
When an RS-232 interface is configured as an MDDB slave, the duplex mode is automatically
set to half-duplex and s-bit-signaling is forced off. When multidrop data bridge is disabled, the
duplex mode is set back to the default of full-duplex and S-bit signaling is turned on (but can
be set back to off).
When either an RS-232 or X.21 interface is configured as an MDDB master, the duplex mode
is automatically set to full-duplex and S-bit signaling is forced off.
Default disabled
Parameters disabled — MDDB mode is off
slave — the port is operating as an MDDB slave device
master — the port is operating as an MDDB master device
Note: An X.21 interface configured as an MDDB slave does not change duplex mode; half-
duplex is not supported on X.21.
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