MODNET Function 16

Check out the Modnet help page: 

I'm a bit confused here.

Writing to a Read/Write register is pretty much what Citect does normally.

Is there some sort of difference between this an a normal read that is escaping me?

It's mostly transparent to the user.

Normal integer writes use either Modbus Function Code 6: Write single register, or FC 16: Write multiple registers, depending on how many tags need to be written.

There are actually 3 classes of modbus function codes. Very simple modbus devices may only support class 0 commands (FC 3: read multiple registers, and FC16 write multiple registers). This is the minimum useful set of functions, for modbus devices. To limit communications to that leve in Citect, you have to set the INI parameter I mentioned to tell Citect to use FC 16 regardless of the number of registers it's writing.

Here's a clip from the Open Modbus/TCP Specification: 

Thanks Eric, does it mean that when I write data in series of consecutive registers will use FUNCTION 16.

TagWrite("Tag1",20)
TagWrite("Tag2",21)
TagWrite("Tag3",22)
TagWrite("Tag4",23)
TagWrite("Tag5",24)
TagWrite("Tag6",25)

Felix

If you set the PresetMultiRegistersOnly parameter, then it should. If you don't set that parameter, then you'd have to test it to know for sure. TagWrite() sends an individual write to the I/O server, so I don't know if they would get grouped together. It's better to just write directly to the tags without TagWrite() and the writes will be sent to the I/O server together:

Tag1 = 20;
Tag2 = 21;
Tag3 = 22;

etc.

Thanks Eric, I will test it.

Felix Custodio Did you manage to test it?

not yet, waiting the actual device to arrive