Qld (Quick Ladder Diagram) Reference

Quick Ladder is a restricted form of ladder programming suited to logic control. The Quick Ladder diagram editor (within the DPL editor) enforces a rigid layout of ladder elements such as contacts, coils and function block calls. Quick Ladder allows a valid ladder diagram to be developed very quickly.

The QLD language supported in SYPT is very similar to the QLD language supported in SYPTLite. The differences are that variables can be used in QLD in SYPT and that multiple QLD diagrams can be created in different tasks in SYPT.

Within SYPT, ladder diagrams can be created in the QLD editor or in the LD/ FB editor. Each editor has its own advantages:-

QLD allows a restricted form of ladder diagram to be created. The editor is very simple to use and automatically lays out the ladder elements. The main restrictions are that contacts and coils cannot be connected to function block inputs and outputs.
LD/ FB provides much greater freedom in creating ladder diagrams. Contact and coils can be connected to function block inputs and outputs and more sophisticated arrangements of ladder elements can be made.
Function blocks do not have an EN input or an ENO output in LD/ FB.

The full set of supported functions and function blocks for a target can be called from a QLD diagram. In addition, user-defined function blocks can be called. It is not possible however, to call subroutines from QLD.

For more information on QLD, see:

QLD Elements
QLD Coil Types
QLD Contact Types

Qld Elements

A ladder diagram is drawn as a list of rungs where contacts, coils and other elements are inserted.

The following is an example of a simple rung with a rung comment. The rung contains a contact and a coil bounded by power rails. Note that variables as well as parameters can be associated with ladder elements such as contacts and coils.

Quick Ladder provides the following elements:

Left Power Rail Example

The left power rail on a ladder rung always enables any elements to the right on the rung. In the following example, parameter #18.31 will always be set to 1 because the coil is always enabled.

Function Block Example

In the following example, a direct contact associated with bit 0 of a variable called Engaged% is being used to selectively enable or disable an add function block. Whenever Engaged%.0 is set the add function block adds 1 to Speed% and writes the new value back to Speed%. When Engaged%.0 has the value 0, the add block is disabled and is not executed, i.e. the value of Speed% is unchanged.

Jump Examples

In the following example, a direct contact associated with parameter #18.31 is being used to selectively jump to the third rung. When #18.31 is set, the contact enables the jump to COPY_BIT, control transfers to the third rung and the subtract block is not executed. When #18.31 is clear, the jump is disabled, rung 2 is executed and 1 is subtracted from #18.20.

The following is an example of an unconditional jump. Since the jump is connected to the left power rail, it is always activated when the rung is executed and so the jump always occurs. A rung like this can be created by clicking the mouse in a blank area below any rungs in a diagram and inserting a jump. A new rung will be created containing a single jump.