Modicon 484 PLC Online Problem

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Thread Starter

Brian Peck

Does anyone have any experience working with the Taylor 484 Online software (DOS based, circa 1980's), and connecting to a Modicon 484 through the J470 converter? The 484 uses a proprietary non-RS232 serial protocol, which the J470 converts to RS232.

The problem that we are experiencing is this: We connect to a running PLC and attempt to view the logic rungs online. Communication times out and then attempts a retry, which also times out. At this point the software allows you to retry, or quit. All attempted retries fail. When you
finally tell it to quit, it shows the first rung on the screen and has "0001/????" at the top of the screen. The software then shows an error
message "Incorrect Address Boundary" and the program locks up, requiring the computer to be powered off.

If the PLC is stopped, you can view the logic in the PLC without any timeouts. Starting the PLC and viewing the logic online is possible if you
have first stopped the PLC and looked at the logic online. It is also possible to upload and download the program if the PLC is stopped.

The processor model is a 484 Model 6 Enhanced, and there is one rack of expansion I/O.

We have run the Taylor software on a Pentium II Laptop, a 486 33Mhz, as well as an original IBM-XT, just to rule out CPU clock speed as a potential problem. Has anyone seen this, or have any suggestions? Modicon Technical Support has not been able to offer any solutions past the possible CPU clock speed being too fast for the Taylor software that expects to be running on an Intel 286.

Brian Peck
Engineer
Northeast Utilities
 
R

R A Peterson

In a message dated 2/28/00 2:56:59 PM Central Standard Time,
[email protected] writes:

<<
> We connect to a running PLC and attempt to view the logic rungs online.
...
> If the PLC is stopped, you can view the logic in the PLC without
> any timeouts. Starting the PLC and viewing the logic online is
> possible if you have first stopped the PLC and looked at the logic
> online. It is also possible to upload and download the program if
> the PLC is stopped.

I don't have any experience with this software but in general my guess is that you have one of two problems.

1) The PLC is loaded to such an extent that it does not respond within the timeout time when online. The obvious solution to this would be
to increase the timeout period (if possible). If you cannot increase timeout then try removing some of the logic (I don't think this would be a real solution but it could prove the problem).

2) There is some "run" protected region that the program attempts to read and PLC does not respond when running. Again not familiar with equipment, but Modicon should be able to tell you if there are any such regions.

>>

1. Modicon 484s only allow downloading to the PLC while it is not running.
This is the normal way all PLCs are.

2. 484 plcs do not have any run protected areas to my knowledge.

3. IIRC, the port on the front of a 484 is current loop. The JXXXX whatever interface converts the PC RS232 port to current loop. Perhaps the JXXXX whatever is defective.

4. This is an obsolete system that would be best to replace with something more modern and more easily supported. As it gets older it will only get more cantankerous. The conversion to a 984 system is straighforward as long as no sequencers were used in the 484.

If you have specific questions, I'd contact modicon tech support at [email protected]. They actually answer email tech support questions
fairly quickly.
 
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