Toshiba T2N - Manual (Page 215)

5. Programming Language
202 PROSEC T2N
5.2
Ladder Diagram Mixed use can be made of the two types of programming language,
ladder diagram and SFC in the T2N. However, of these, ladder diagram
is the basic language which must be present in the user program.
Here, the structure, execution sequence and general items of ladder
diagram instructions are explained for ladder diagram programs.
As explained before, a user program is registered by every functional
type which is called a program type. Furthermore, in each program type
the user program is registered by one or a multiple of units called
‘blocks’.

Main program, sub-program #1, timer
Program Types ...

interrupt program, I/O interrupt programs #1-#4,

sub-routine.
Blocks .......... Blocks 1-256 (1 language/1 block).
When commencing programming in a block to be newly registered, that
program is designated by the language which is used (this is called
‘language designation’).
However, in the case of ladder diagram, the operation of language
designation is not required (the default is ladder diagram).
The ladder diagram program in any one block is registered/arranged by
units called ‘rung’. A rung is defined as 1 network which is a combination
of lines connected to each other, as shown below.
Rung number
Rung