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Modbus FIFO Read Function

Hello everyone :

I just implemented Modbus function 24 on my drive controller (slave) (as a kludge to access extended data for parameters mapped to holding registers)

The problem is I can't find anything to test my slave implementation - I have coded something, but of course this is derived from my own understanding of the standard.

Does anybody know of a third-party program that uses this Modbus function to test my slave implementation

Thanks

Gary

Reply to
Gary Pace
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From the MODBUS Protocol reference guide, page 70, it states the function is only supported by 984-785 controllers and for reading FIN/FOUT function blocks.

That is a tad specific to find in a non PLC manufacture program.

As a slave, who is the master and can it not read use this function? If you do not have a master to read then what is the point?

I am confused. ;)

Mark

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Mark :

Thanks for your reply.

Actually, I am using this function as a way of obtaining extended information regarding system parameters (which are mapped as holding registers on modbus). So holding register N is the run-time value, and FIFO N returns attributes such as max, min, default etc. We are going to write the master function in our host, which will use MODBUS (RTU, over TCP or over USB) to monitor the drives.

So, we will write our own master. I just wanted to have a third party source to verify my implementations (I use Modbus poll to check some of the standard functions)

I didn't notice the very limited implementations of this function, so I guess it's a moot point.

Gary

Reply to
Gary Pace

I used Modscan32 from Win-Tech Software

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Unfortunately, to use that program, you would need to write a custom script that is sent since your function is not one of the more "normal" Modbus functions. I had to do that for a few functions our customer wanted implemented that Modscan32 did not support. It is sort of a pain to do, but it does work. I think custom scripts are a one-shot deal and must be manually executed each time, as opposed to other functions that can repeat ever N milliseconds. Even so, it can be used to test the function, and at $65 it might be worth it.

Lou

Reply to
Mr. C

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