Rockwell Automation 9323-S5500D A.I. SERIES MICROLOGIX 1000 AND PLC-500 SOFTW User Manual

Page 374

MicroLogix 1000 and PLC-500 A.I. Series Software Reference

15-38

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Problems with special or advanced features such as data compression and high

speeds.

If your modem switches to 14.4 Kbaud or starts compressing data, the

KF3 and PLC-500 A.I. may run into problems. A modem (through data

compression or otherwise) which switches to a higher communication rate to boost

performance will likely result in intermittent communications, or none at all.

If you run into initialization problems, try disabling these features. If you haven’t

purchased your modems yet, try to purchase identical modems for this task.

Ideally, you should purchase 9600 baud modems with no data compression.

Identical modems may automatically enter data compression mode. To avoid this,

disable automatic data compression on your modems.

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CD and DTR problems.

Some modems will hold the CD (Carrier Detect) and

DTR (Data Terminal Ready) lines high all the time. This will conflict with the

operation of the PLC-500 A.I. software. If you are trying to use modem dialing,

and the software doesn’t even try to initialize the modem, then the CD or DTR

lines are probably held high. When PLC-500 A.I. sees the CD high, it assumes

that a connection is already made; and won’t bother to try to initialize

communications and dial your number.

To circumvent this problem, you must send a command string to the Hayes

compatible modem. Use the Terminal Utility Program as a dumb terminal to send

the following string to the modem:

AT&C1&D2&W

[Enter]

The

&C1

puts the CD line into normal mode. The

&D2

puts the DTR line into

normal mode. The

writes these changes to ROM so you won’t have to issue

this command every time you use the modem (don’t use the

if your modem does

not have that feature). (Check your modem’s owner manual for more information

about command strings.)

After entering this string, the software should be able to dial correctly. If it still

cannot, try dialing manually from the Terminal Utility Program. (For more

information, see the

Terminal Utility Program

section on page

15-39

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