Watlow 12LS Controller - Manual (Page 32)

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3.5.3.2 RS-485 CONNECTIONS
Connection of ANAFAZE controllers to a system computer requires an interface at the computer to convert RS-232
levels to RS-485. Anafaze recommends Black Box Model LD485A for this purpose. The LD485A should be
configured for DCE operation, with the RTS/CTS delay jumper in the "on" position. ANAFAZE can supply this
converter configured and checked out with the system on request.
Normal Operation LD485A installation setup:
1. DCE operation (Dip shunt in XW1A socket)
2. Normal operation (Front panel switch out)
3. Full Duplex operation (Jumper W8 on Full)
4. RTS/CTS Delay set to ON (Jumper W9 to ON)
5. Unterminated operation (Switch S2 to Unterm)
6. No jumper at position W7
The RS-485 specification is for "balanced line" operation, and is not true differential. Thus a common connection is
required between all stations on the communication line. This can be accomplished by either a 5th wire (which could
be shield) or a common ground connection.
The ANAFAZE system more conveniently supports the common ground connection, although 5th wire can be
supported if required due to common mode voltages generated in a given installation. The 3rd wire connection would
be required only if the "common mode" voltage between stations exceeds the RS-485 specification of 7 volts peak.
To make sure the communication system works, the controller chassis must be electrically tied to Earth ground, and
the host computer communication must be tied to Earth ground. If the host computer RS-232 communication is not
referenced to Earth ground, install the 100 _ resistor in W7 as recommended by Black Box.
The following diagram shows the recommended system hookup. The transmitter from the host computer connects in
parallel to the controller receivers, and the host computer receiver connects in parallel to the controller transmitters. A
single "daisy chain" is recommended. Octopus connections or "spurs" are discouraged. A termination resistor is
required at each end of the transmission line. This is accomplished by applying a 200 _ resistor across the line at the
farthest point from the computer transmitter. Check with ANAFAZE for setting the Black Box SW2 to the "term"
position to terminate the computer receive line.