How to Use the Step Ladder Program Block
Appendix 1
206
Note 1
The execution cycle of sequence commands in the Step Ladder Program block is slower than
the execution cycle (cycle time) of commands on the CPU Unit. (0.1 to 2 s cycles follow the
operation cycle of the Step Ladder Program itself.) For this reason, the Step Ladder Program
block is used combined with other function blocks. When high-speed processing is required,
use commands on the CPU Unit.
At the Step Ladder Program block, external contacts are not directly input and output. They
are input and output via Field Terminal DI or DO terminals.
WARNING
When the OUT instruction from the Step Ladder Program is to be connected to a DO
terminal, do not set the address for the OUT instruction from the Step Ladder
Program to the same address as the address for the OUT instruction in the user’s
program on the CPU Unit. When writing is performed on identical addresses, the
externally connected load may act unexpectedly and cause injury.
A single sequence command (e.g. LOAD or OUT) is described to a single ITEM, and the block address and
ITEM number of the specified input/output destination are described at the same time as the operand.
Sequence commands are described as a command code within the range 00 to 30. There are two types of
sequence command, basic instructions, and sequence control instructions. Basic instructions can be used
only in logical sequences comprising single steps, and sequence control instructions can be used in step
sequences comprising multiple steps.
ITEMs that can be specified by sequence commands are ITEMs whose ITEM category is "contact input" or
"contact output." For details, see the Setting Method item in the ITEM lists in the descriptions for each
function block.
Command type
Settable ITEM type
"According to Step Ladder Program" at
"Settable Method" Item
Contact output
R (read-enabled)
Input type commands
such as LOAD
Contact input
Output type commands
such as OUT
Contact input
R/W (read/write-enabled)
