Micrologix 1400 Input/Output Oddity

Ignition
1

I have a Micrologix 1400 BXBA that is set up in my Ignition gateway. I can browse to the input (I) and output (O) locations through the OPC browser. For the most part all works as expected. I decided to set up all the embedded I/O in my SQLTag tree for use with some testing I am going to be doing. This is where I uncovered a bit of a head-scratcher…

On the input side, I pulled in the 16 bits in word 0 (I:0.0/00 - I:0.0/15). These all work fine as I actuate the inputs on the PLC. However, when I pulled in the 4 bits in word 1 (I:0.1/00 - I:0.1/03), they did not work as expected. What’s more, is that it seemed to make some of the other bits act funny as I watched my tag tree in the Designer (e.g. bits turning on and off unrelated to the specific input I was manipulating). As soon as I removed these 4 bits from the tag tree, everything was fine again. Then I added the 4 words representing the analog inputs (I:0.4,.5,.6,.7). The subscription to any or all of these words yielded equally anomalous behavior. And likewise, dumping them returned things to normal.

On the output side, this came up again in similar fashion. Now all the outputs on this model fit in word 0 (I:0.0/00 - I:0.0/11) so the digital outputs were all fine. Then adding the 2 analog inputs (O:0.4,.5) made things act weird. In RSLogix, I can see it try to set the word to the correct value (it did) but then after the gateway polled the tag again (1 second scan class) it reset to a value of 1.

Is there a limitation to the built-in ML1400 driver that would cause these issues when accessing anything outside word 0?!

2

We ran into this with the ML1100s as well.
I suspect it has to do w/ the different base models of the ML1100 and ML1400.

I think we managed to work around it by making sure the program in rs500 knew exactely which model I was using.
But I think I had more luck mapping I/O to B and N datatypes.

3

Yes, if I set up a rung to MOV from a value (say N7:X) into the particular analog word, then I’m good. But it still begs the question “why?” I mean, it really acts crazy when you have subscribed to anything other than word-0 stuff. The minute I do something outside of word-0 it not only ‘doesn’t work’ but it also makes the working stuff (word-0) act up. I’d tick the boolean on O:0/0 and then it wouldn’t actuate the relay and after a second, the checkbox in the tag tree in Ignition would uncheck, etc…