MKS Stabil-Ion 370 Series, Инструкция по эксплуатации, Страница: 52 / 122

3 Installation
3-16
Series 370 Stabil-Ion Instruction Manual - 370119
3.9 Connecting the RS-485 Computer Interface
Instructions for setting up this interface are in Section 2.1.5 on page 2-12.
The RS-485 communications option permits data output to, and gauge control by, a host computer
using RS-485 digital communications. Communications handshake is by a command-response
mechanism.
Information on Commands begins in Section 4.14 on page 4-33.
Connectors J1 and J2, Figure 3-13, on the rear of the control unit are wired parallel and are
interchangeable. Connection can be made by daisy chaining gauge controllers together with the
signal from the host computer going into one connector, then out the other connector to another
gauge controller.
The maximum total cable length is 4,000 ft. No more than 32 devices can be connected to one RS-
485 communications line. When an RS-485 network is in an idle state, all nodes are in listen
(receive) mode. Under this condition there are no active drivers on the network. In order to
maintain the proper idle voltage state, bias resistors must be applied to force the data lines to the
idle condition. Figure 3-14 illustrates the placement of bias resistors on a host computer, 2-wire
configuration, for the typical 5 volt and 24 volt systems.
In a four wire configuration connect TX on the gauge controller to RX on the host computer and
connect RX on the gauge controller to TX on the host computer. If the computer sends and receives
data on 2 wires, connect the RS-485+ from the computer to both the +TX and +RX (pins 4 and 8),
and connect the RS-485 from the computer to both -TX to -RX (pins 5 and 9). Figure 3-15 shows the
proper wire connections for a 2-wire connection.
When connecting multiple Series 370 Controllers connect TX to TX and RX to RX on all controllers.
The polarity may have to be reversed on the computer and other instruments—you may have to try
it both ways. No damage will result if connections are wrong.
Figure 3-13 RS-485 Connector