ML1100 modbus

Alan Case

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Apr 2002
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Hi. I have a Kingfisher RTU connected to 3 ML1100's using modbus.
The ML1100's are set as slave units and the Kingfisher as the master.
The Kingfisher sends data to the ML1100's which are receiving the data most of the time. The messages get sent approx every 5 seconds but arrive between 5 and 100 seconds apart. The status of the comm port in the ML says there is link code error 4 and 5 (parity or UART framing error).
Is there something to connect inline to analyse the messages or any other ideas on the problem.
Regards Alan Case
 
Serial communications diagnostics is definitely a theme this week.

How are the Kingfisher and the MicroLogix connected together; some kind of RS232/485 converter, or radios, or something else ?

What are the port settings (baud rate, parity setting, stop bits) for the Kingfisher and for the MicroLogix ?

It sounds like a wiring or transmission issue more than anything else; if the master is sending data every 5 seconds but it's not being received 95 % of the time, there has to be something physically incorrect.
 
The Kingfisher is set as the master and sends data to the ML1100s every 2 seconds. That is I send data to PLC A, when done or errored I send to PLC B, when done or errored I send to PLC C. I wait 2 seconds and start again.
From the help file "Kingfisher RTUs use a data format of 8 data bits, no parity bit and 1 stop bit and support the 'RTU' Modbus data format."
The ML1100s are set to node 91, 92 and 93.
Each ML1100 has a 1763-NC01 plugged into channel 0.
The units are connected via cabling of total length 8 metres. I have a 120 ohm resistor accross each extremity of the 485 network.
In the RTU I increment a register from 1 to 1000 with an increment of 1 every second. The time that I see the value change in a ML1100 varies from 8 to 35 seconds with link layer errors as per the attachments.
The attached files are jpg files not zip files. Please change the extension.
Regards Alan Case
 
Last edited:
there is any possiblity to increase the baud rate


test the ML1100 with MODSCAN utillity to troubleshoot wherther the problem is from ML1100
 
Hmm.

RS-485 can run over a wide variety of cabling, especially for the short distances you're talking about.

1761-NET-AIC's and 1763-NC01 cables usually terminate the network with jumpers between terminal 5 and terminal 6. There's an internal 120 ohm resistor in the NET-AIC or -NC01 that is connected between Data A and Data B using that jumper.

The new MicroLogix 1100 firmware FRN4 has selectable parity and stop bits for Modbus RTU protocol, but it sounds like 8 data bits, no parity, 1 stop bit are the standard settings for FRN3.

This really sounds like a signal problem to me.

Does the Kingfisher have a native RS485 interface, or is there a 232/485 converter on that end ?
 

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