Modicon 984 LL Blocks & Tables

I am new to Modicon PLCs. Can anyone please explain what exactly a "Block" and a "Table" are in Modicon 984 Ladder Logic? I have looked through the documentation but don't see anything obvious. Maybe I am over thinking this as I believe in the Quantum CPU there is simply a long array of registers. An example would help as well. Thanks!

Bump...

I think a block is like a word in other software. Notice that there is no MOV instruction in ProWorx, it's BLKM.

Both the word "Block" and "Table" may be used to describe a group (or array) of registers. What is unique about a Table is that it has a pointer associated with it that allows data to be read or written to or from a specific register (or Registers) within the Table.

A "Register to Table" function will move the value from a specific source Register to a specific location within a Table.

A "Table to Register" function will move the value from a specific location within a Table to a specific destination Register.

A "Block to Table" function will move values from a specific group of source Registers (A Block) to a specific starting point location within a Table.



The word "block" can also refer to a function block, such as a math or data move function that may be utilized in ladder logic.

Thanks for the explanations. The more I get into the Modicon 984 LL the more I see it has many differences from RA. The inverted scan method, no latch/unlatch instruction capability, coils that can be true from a timer that is not even connected to the power rail, postive transition contact that shows it is true even after it is false, etc. Standard code practices I have used for years goes right out the window. Interesting how many people say this platform is the best...I guess it is just what you learned first and are comfortable with.

aiki202 said:

Thanks for the explanations. The more I get into the Modicon 984 LL the more I see it has many differences from RA. The inverted scan method, no latch/unlatch instruction capability, coils that can be true from a timer that is not even connected to the power rail, postive transition contact that shows it is true even after it is false, etc. Standard code practices I have used for years goes right out the window. Interesting how many people say this platform is the best...I guess it is just what you learned first and are comfortable with.

Click to expand...

Yes. People tend to prefer what they are most familiar with.

remember that 984LL is at least 20 years old.
The new modicons all use an IEC based programming format

GeoffC said:

remember that 984LL is at least 20 years old.
The new modicons all use an IEC based programming format

Click to expand...

Even the older Quantum PLCs that I've been working with recently use function block programming, rather than ladder logic. They do still support RLL though.

984LL started with or before the Modicon 584 and continued upto the quantum range. With the Quantums (depending on the model) you could use the 984 OS and program with Proworx or you could load it with the iec os and use Concept and now Unity. The iec os has all 5 formats (Ladder, Function block, Structured Text, Instruction List and SFC).
Recently they have added the 984LL format to Unity so that programs could easily be ported to more up to date hardware.