write this for me for cashola?

ganutenator · Nov 11, 2015

I will most certainly have to clarify this in more detail, but here goes.

Talking modbus at 19.2k to 6 Altivar 312 vfds and 2 Altivar 212 drives, currently.

Problem:
Need to add more reads and writes, but don't want to affect the critical writes during machine motion.

Want:
Someone to write a function using the read_var and write_var in Unity that allows me to give certain writes/reads different priority, loops through others, allows me to put an enable bit on the data I want read/written.

tragically1969 · Nov 11, 2015

As usual, first question, what PLC, I presume Schneider and i presume M340 or Premium ?

How do you intend somebody write a program that let's you write when and where you want but not interrupt the comms already going on ?

Either you need to drop your new read_var and write_vars into the existing comms cycles then enable when you need them to be used or stop the critical writes happening so you can write your non critical ones ?

Either way it shouldn't be too hard to do with a little thought and planning.

ganutenator · Nov 11, 2015

yup, M340.
"shouldn't be too hard"
how much ?

ganutenator · Nov 11, 2015

I could do it, but it would take me a long time.
I've been writing plc code for 18 years, but maybe I'm getting old and stupid.

tragically1969 · Nov 12, 2015

ganutenator said:
yup, M340.
"shouldn't be too hard"
how much ?

Impossible to say without seeing the existing code. Do you need to keep the PLC running while the change is made or is there some downtime to get it in and test it ?

If all the drives are same family it may be better to go Ethernet on the drives and add an NOE card on the M340 then just I/O scan them.

ganutenator · Nov 12, 2015

would love to go Ethernet. And we are already using an NOE card. Problem, is the ethernet add on to the ATV312 costs more than the drive.
Looking to write a user defined function block for future versions. (aka no reason I can't download the entire program as an update).

The DFB would do reads and writes in a loop, but then would insert the registers to read and write on a priority and enabled input preference.

ganutenator · Nov 12, 2015

and I prefer the dfb to be written in structured text

Highland Controls · Nov 13, 2015

I guess I would question what critical motion writes are happening over Modbus, and should there be anything critical happening over Modbus.

ganutenator · Nov 13, 2015

critical

Critical would be the estops.
just kidding
I would like the speed command changes to take priority over lets say, reading drive status.

ydtech · Nov 13, 2015

I take it you have some criterion for when the machine is in a critical state or not. Write the extra stuff and slot it in between the criticals whenever the machine is safe, disable when it's moving.

If there's a lot, use a counter and comparators to stagger them, one for each scan or other period of your choice.

PLC GURU · Nov 13, 2015

pretty easy... just look for change in states (on your critical messages) then stop the loop. and perform the writes. I usually always do a constant loop for the reads and interrupt it when I have a write.

write this for me for cashola?

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