FX3U and 2x 485adp-mb

3 posts in this topic

Hoping this is an easy one....

I have an FX3U-80 with 2x 485adp-mb cards on the side. The intention is for one to be a slave and the other a master to read from a slave. 

I have successfully got CH2 (the outer card) working as a slave so no issues there.

However I seem to be hitting a few speed bumps (OK, road blocks) with using CH1 as a Modbus master. The last time I did this was with an IEC program and Q series- so I could use the intelligent module setup window. This time I am using basic ladder and an FX3U. I only want to read about 6 registers from the salve device and can set its node address to whatever I like, but typically I'd use 2. Does anyone have an example code to hand they could pop up? 

Here is what I've got so far in relation to the master..... pretty much taken from the "Modbus Serial Communication Edition" FX3 manual.

Now there is a chance (admittedly a pretty good one) that I'm being thick as pig poop as I am not currently connected to an actual slave device, instead I have the port plugged into a 485 converter and have been using modscan32 on my laptop- this reads from my slave port perfectly.  I was hoping to see some or any comms/ flashing SD or RD lights this way. I will be hooking up to the actual device tomorrow so maybe it'll come to life.... or not?!

Thanks in advance. If I manage to sort it myself in the meantime I will post up and hopefully highlight the solution/ issue. 


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OK, update for anyone else in this position.

Turns out that you can't have a slave and master on the same FX3 cpu; the slave function takes priority and knocks out the Master. I have my local dealer's top man (and he is sh$t hot) writing some code to use the master port as an RS-485 port as opposed to Modbus function. 

The worked example in the FX3 modbus manual (around page 114) works so it can be used as a reference if there are problems with setting a master.

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I have used the FX3U several times with one Modbus RTU Master and one slave.

I used one FX3U 485BD(ch1 master) and one FX3U 485ADP-MB(ch2 slave).

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