MicroLogix 1400 and reading Binary Files (e.g., B3:0/1 or B45:0/11)

Cory Podojil

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Sep 15, 2021, 6:59:43 PM9/15/21

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Kyle (and pals)!! Absolutely digging you hard work here, great stuff! Very much appreciated.

I find myself stuck while attempting to read bit values from a MicroLogix 1400 PLC. Here's the tags:

B3:1/3

B45:0/11

B3:0/14

I am able to perform a plctag.plc_tag_get_bit(id, 0) to return 0/1 but if I add change the offset I get a 'Data offset out of bounds!' error. Using the .NET wrapper, it's always false (unit8 conversion issues?).

Background: using the libplctag.NET C# library, works exceptionally well for ControlLogix but no luck thus far with MicroLogix 1400/SCL500.

Debug logs attached for B45:0/11:

WithOffset.txt - offset == 11

WithoutOffset.txt - offset == 0

Thoughts/guidance?

Thanks,

-Cory

WithOffset.txt

WithoutOffset.txt

Kyle

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Sep 17, 2021, 11:08:18 PM9/17/21

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There seems to be a problem with MicroLogix and binary files. I just got a MicroLogix (today!) so I hope to figure out how to get it working and then I can test this. I was able to get some dumps before and one of the things I saw is that the library is requesting only one byte and should be two.

When a single bit is being accessed the library needs to read a full INT (2 bytes) and then mask off the right bit. This is not well supported yet. It is on the list to fix and does appear to work correctly on PLC/5 systems.

Best,

Kyle

Cory Podojil

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Sep 18, 2021, 3:56:08 PM9/18/21

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Oh sweet! Glad you got your hands on the device! Let me know if I can help with testing or more debug logs.

Kyle

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Sep 22, 2021, 12:20:10 AM9/22/21

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Still trying to find time to set it up. I have MicroLogix 1100. That was the cheapest thing I could find with Ethernet.