MKS Granville-Phillips 358 series, Instruction Manual

Page: 42 / 122

Chapter 3
42
Series 358 Micro-Ion Controller Instruction Manual - 358013 - Rev. B
3.13 RS-485 Computer
Interface Setup
If your Controller does not have this capability, skip to Replacing the
Controller Cover on page 47.
RS-485 capability permits data output to, and gauge control by, a host
computer. Output is by a command-response mechanism. If you have this
module in your unit, configure it to your system requirements by setting the
switches as instructed in
Selecting Byte Format for RS-485 Module on
page 46.
A variety of baud rates and byte framing options are available, as well as
switches to force the handshake lines to an “always true” condition.
The controller RS-485 factory defaults are: 19.2Kbd, 8 character bits, no
parity, 1 stop bit, address = 01.
Internal switches are read upon controller power up. Changes in settings
will take effect upon next power-up cycle.
Connector Pinouts for
RS-485 Computer
Interface
Connectors J1 and J2 on the rear panel are wired in parallel and are
interchangeable. Connection can easily be made by “daisy chaining” gauge
Controllers together with the signal from the host computer going into one
connector then out the other to another gauge Controller, and so on.
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. To maintain the proper
idle voltage state, bias resistors must be applied to force the data lines to the
idle condition. Figure 3-16 illustrates the placement of bias resistors on a
host computer, 2-wire configuration, for the typical 5 volt and 24 volt
systems.
Table 3-10 RS-232 Controller Outputs
Line Pin Description Internal Switch Function Factory Setting
RTS 2 REQUEST TO SEND:
De-asserted by controller on
power-up. Asserted by
controller upon receipt of a
message terminator as a
holdoff to prevent the host
computer from attempting to
transmit data until the
message just received has
been parsed and a reply has
been output. De-asserted
after transmitting the
terminator of controller's
response to that message. INVERT RTS: When OFF
inverts the polarity of the
RTS line allowing
nonstandard connection
directly to host computer
CTS line. When ON, set to
operate as a modem line per
RS–232 standard. ON