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talk to AB SLC 5/03 PLC

I'm trying to communicate with an old Allen Bradley PLC "SLC 5/03" via the DB9 port set up as DF1- full duplex with Lookout 5.1. I'm using a native serial port on my computer running Lookout.


There is no way to 'see' anything inside the PLC.


Any previous experiences of anybody?



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Message 1 of 9



I've used that method before with no problems once the port parameters are set correctly. Make sure that your port configuration on the PLC matches that of Lookout or vice versa. The PLCs port parameters are set in RS Logix. If RSlogix can talk to the PLC through the serial port Lookout should also. One common mismatch is the error checking parameter CRC or BCC. Also rember that the Lookout driver objects addressing scheme is slightly different from what you might expect for the physical I/O. You might need to check the driver object help file.


Jim Besselman



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Yes, you are right on that. I found the problem and now Lookout is talking to the PLC.


There a new issue: I can read/write variables in the PLC itself, but There is no way to read from the I/O Modules attached in the same rack.


The rack is a 7 position rack. After the PLC there are 2 modules 1746-IV32, 2 modules 1746-OA16, and 2 modules 1746-N14.


I have tried several ways (Syntax) but I have nothing so far.


Any suggestion?

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Message 3 of 9



From the Help File


Lookout has adopted a sequential, flat addressing scheme for the Allen-Bradley PLCs. The addresses are sequential by data type, having nothing to do with the actual slot number. For example, consider the following slot configuration:

PLC slot Location    Type of Module in PLC Slot    Channel Address in Lookout
slot 1    16 channel analog input    I:0-I:15
slot 2    16 channel analog output    O:0-O:15
slot 3    8 channel input, 8 channel output    I:16-I:23, O:16-O:23
slot 4    16 channel analog input    I:24-I:31
You can see from the example, the slot number of the module is irrelevant to Lookout, and the input channels follow consecutive numbers as the output channels follow their own consecutive numbers. Input and Output word addresses are 0 based.

So if your slot 1 is 1746-IV32 I think it will map to I:0_0 thru I:0_15.

The next 1746-IV32 would be I:1_0 thru I:1_15.

The outputs would be O:0_0 thru O:0_15 and O:1_0 thru O:1_15.

The 1746-NI4 would be I:2 thru I:5


If you start dragging datamembers from the driver object you'll figure it out


Jim Besselman

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For DIGITAL inputs and ouputs modules it does work well. My configuration is:

2x32 digital inputs (1746-IV32) these are I:0, I:1, I:2, and I:3 (words)

2x16 digital outputs (1746_OA16) these are O:1 and O:2 (words)

As soon as I try to setup the following analog input modules in Lookout, seems like communication drops, I got red crosses over the display of the words.

Analog inputs are 1746-N14 (two of them) 

According to your explanation they should be I:4, I:5, I:6, and I:7 for the first module and I:8, I:9, I:10, and I:11 for the second.


Thanks again.

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I'm puzzled as to why your 1746-IA16s aren't at O:0 and O:1. Do the analog modules also have output words associated with them. I'll find my old file and see how it was set up but it will be a few days before I can get to it.



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One more thought, can you pull the digital modules and try a configuration with just the analogs?



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Message 7 of 9

The syntax is correct as Jim described. I did a test here with an NIO4 module and IO8 module. The two AI on NIO4 are I:0 and I:1, the inputs on IO8 on second slot are I:2.  


Maybe to test NI4 individually is a good idea. Just install NI4 on first slot without any other module, and use I:0~3 to read data.

Ryan Shi
National Instruments
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Message 8 of 9



Analog modules are not good at the end of the rack. I got that.

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Message 9 of 9