PLC 5 Messaging

I have seen a lot of info on this site, on the best way to set-up 'Messages', to acheive the best speed, dependability, and not drag down the DH+. Can I see some suggestions, on what works the best?

I only trigger my MSG blocks when I need to send the data out.

For instance, if you are sending a number from 1 processor to another, only trigger the MSG block when that number changes.

You can set up the 1 MSG block to write the data and another to read the data back to make sure it got there safely.

Also if possible, up your baud rate to 256 instead of 56. They will also speed up your through put.

MSG data.

It depends on the size of your DH+ network and how much data is sent between PLCs. A Large block is better than many small blocks. Send the data only when you need it. I see people programming the MSG block to update every scan, this is not a good idea. If the data is updated every second, do you really need the data in the other PLC every second? Are you sending interlocks or just integers? Do you want to check the integrity of the communication? There are a few good ways to do this. A timer counting in one PLC that is reset with each MSG block from another PLC is one way. Without the reset an alarm is set.

On the point of controls and interlocks..There is a time delay even on the smallest network with the highest speed.
I make it a daily routine to check the networks on the PLCs for problems. Are there a lot of errors? If your DH+ is a star configuration, MSGing will start to show a lot of errors on the network.

These are a few points to consider on your MSG programming.

Im sure there are others on here who will add to this.

I support one production area with three 5/80E's networked together via DH+, ethernet is used for the HMI's.
I cascade my messages. I use the done or error bit of MSG-1 to start MSG-2, and so on, then the last message starts the first message. I usually use the first pass bit in parallel to get the cascade going on the first MSG-1.



Ken