Semi-graphic form | Full graphic form | |
A horizontal link along which power can flow | ||
Interconnection of horizontal and vertical power flows | ||
Left-hand power connection of a ladder rung | ||
Right-hand power connection of a ladder rung | ||
Normally open contact | ||
Normally closed contact | ||
Positive transition-sensing contact, power flow occurs when associated variable changes from 0 to 1. | ||
Negative tranistion-sensing contact, power flow occurs when assoaciated variable changes from 1 to 0 | ||
Output coil: if the power flow to it is on then the coil state is on | ||
Set coil | ||
Reset coil | ||
Retentive memory coil, the state of the associated variable is retained on PLC power fail |
Semi-graphic form | Full graphic form | |
Horizontal and vertical lines | ||
Interconnection of horizontal and vertical signal flows | ||
Crossing horizontal and vertical signal flow | ||
Blocks with connections | ||
Connectors |
BOOL is a Boolean signal, INT is an integer, REAL is a floating point number, ANY is any form of signal | |
Up-counter counts the number of rising edges at input CU. PV defines the maximum value of the counter. Each new rising edge at CU increments CV by 1. Output Q occurs after set count. R is the reset. | |
Down-counter counts down the number of rising edges at input CU. PV defines the starting value of the counter. Each new rising edge at CU decrements CV by 1. Output Q occurs when count reaches zero. | |
Up-down counter. It can be used to count up on one input and down on the other. | |
On-delay timer. When input IN goes true, the elapsed time at about ET starts to increase and when it reaches the set time, specified by input PT, the output Q goes true. | |
Off-delay timer. When input IN goes true, the output Q follows and remains true for the set time after which the input Q goes false. | |
Pulse timer. When input IN goes true, output Q follows and remains true for the pulse duration specified by input PT. |
Start step. This defines the step which will be activated when the PLC is cold-started. | |
Transition condition. Every transition must have a condition. One that always occurs should be shown with the condition TRUE. | |
Step in a program | |
Every step can have an associated action. An action describes the behavior that occurs when the step is activated. Each action can have a qualifier: N indicates the action is executed while the step is active. If no qualifier is indicated it is taken to be N. | |
Selective branching | |
Parallel branching when the transition occurs | |
Convergence when both transitions occur | |
Simultaneous convergence |
LD Start a rung with an open contact
LDN Start a rung with a closed contact
ST An output
S Set true
R Reset false
AND Boolean AND
ANDN Boolean NAND
OR Boolean OR
ORN Boolean NOR
XOR Boolean XOR
NOT Boolean NOT
ADD Addition
SUB Subtraction
MUL Multiplication
DIV Division
X:= Y Y represents an expression that produces a new value for the variable X.
(…) Parenthesized (bracketed) expression
Function(…) List of parameters of a function
** Raising to a power
−, NOT Negation, Boolean NOT
*, /, MOD Multiplication, division, modulus operation
+, − Addition, subtraction
<, >, <=, >= Less than, greater than, less than or equal to, greater than or equal to
=, <> Equality, inequality
AND, & Boolean AND
XOR Boolean XOR
OR Boolean OR
IF … THEN … ELSE is used when selected statements are to be executed when certain conditions occur.
The FOR … DO iteration statement allows a set of statements to be repeated, depending on the value of the iteration integer variable.
The WHILE … DO iteration statement allows one or more statements to be executed while a particular Boolean expression remains true.
The REPEAT … UNTIL iteration statement allows one or more statements to be executed and repeated while a particular Boolean expression remains true.
3.21.21.47