Watlow CAS - Manual (Page 38)

28 CAS User’s Guide
Installation
Serial Communications
The CAS is factory-configured for RS-232 communications. However,
the communications are jumper-selectable, so you can switch between
RS-232 and RS-485. (See Configuring Communications below.) You
can also order a communications cable from Watlow Anafaze or make
your own cable.
RS-232 Interface
With RS-232 communications, you can connect the CAS System
directly to the serial communications connector on an IBM-PC or
compatible computer. (PC-compatible computers typically use RS-232
communications.) The RS-232 interface is a standard three-wire
interface. (See the table below for connection information. Some
computers reverse transmit (TX) and receive (RX), so check your
computer manual to verify your connections.)
You can use RS-232 or RS-485 communications in these situations:
• When you are using local communications (up to 50 feet).
• When you are using a single CAS system.
If you use RS-232 communications with grounded thermocouples, use
an optical isolator between the system and the computer.
This table shows RS-232 connections for 25-pin and 9-pin connectors.
RS-485 Interface
• If you use more than one CAS System, you must use RS-485 com-
munications.
• If you have connected the CAS System to a computer more than 50
feet away, Watlow Anafaze recommends that you use RS-485 com-
munications.
If you use RS-485 communications, attach an optically isolated RS-232
to RS-485 converter to the computer. You can use an internal converter
card or an external plug-in converter.
The diagram below shows the recommended system hookup. To avoid
ground loops, it uses an optically isolated RS-232 to RS-485 converter
at the host computer. It is powered from the CAS System's power source
or from a secure, isolated power supply.
DB 25
Connector
DB 9
Connector
CAS Back TB
Anafaze
Cable
RX Pin 3 RX Pin 2 TX Pin 26 White
TX Pin 2 TX Pin 3 RX Pin 25 Red
GND Pin 7 GND Pin 5 GND Pin 23 Black