The Structured Text (ST) language is among the languages of the IEC 61131 standard supported by PLC3000. Compared to other languages like Instruction List (IL), ST supports expressions with a higher level of abstraction. It notably provides loop statements. However, the use of loops is generally considered a poor practice when programming programmable logic controllers […]
Loops – ST
The Structured Text (ST) language supports 3 kinds of loops: FOR … DO … END_FOR: Reapeats some processing for some given iteration count WHILE … DO … END_WHILE: Repeats some processing while a condition is true REPEAT … UNTIL … END_REPEAT: Performs some processing at least once, then repeats it until some condition becomes true […]
Principles of Sequential Logic
Sequential logic functions Sequential logic functions are time-dependent. They define the state of output variables according to the combination of input variables, and also by the memorised state of one or more variables. They are often synthesised by flip-flops. The interest of the sequential logic functions is demonstrated thanks to some examples. Basics of sequential […]
Principles of Combinatorial Logic
TheoryCombinatorial logic is used as a basis for the design of functional programming languages. It responds to a theoretical model. The information is of binary type. It is represented by electrical signals with 2 states {0; 1}. A logical function defines the state of output variables according to the combination of input variables, without taking […]
Automaton Properties
IEC 63111-1 compliant PLCs, such as the PLC3000 solution, are characterised by a cycle operation. A cycle is generally composed of 5 phases: 1. reading inputs, 2. scanning the program, 3. writing outputs, 4. communication services, 5. internal functions. The scanning of the program is always done from top to bottom and from left to […]
Edge generation in LD
PLC3000 with the Ladder langage allows the rising and falling Edges. Declaration in LD A rising Edge is defined during the variable declaration in the Ladder code editor. A rising Edge on input %I0: A falling Edge is defined during the variable declaration in the Ladder code editor. A falling Edge on input %I1 :
Timer – LD
The IEC 61131 standart offers a definition of Timers. PLC3000 integrates only TON timers that can be set by defining the time base %Ti.TB, and the preset value %Ti.PV. The timer is triggered by activating the input %Ti.IN, and the output %Ti.Q goes to 1 when the current timer value reaches the preset value. The […]
Mnemonics in the LD Language
At each variable can be associated a mnemonic. It is then possible touse the mnemonic or variable completely transparently in programs. To associate the variable Switch to the input %I0, the variables RedLight and GreenLight to the outputs %Q0 and %Q1 respectively, it is possible to specify them during the variable declaration in the Ladder […]
Counter LD
The IEC 61131 standard offers a definition of Counters. PLC3000 integrates up and down Counters. It is necessary to define a preset value %Ci.PV, which can be set with an integer value. The current value of a counter is set to 0 when %Ci.R is activated. The current value of a counter is set to […]
Programming in LD
1. Example in ST Let’s considering the logical equation: %M0 = %I0.%I1+%I2. /%I3 2. Example of Grafcet in ST Let’s considering the elementary Grafcet a. Programming Transition/Transition Initialization Test on Receptivity and Transition Crossing Output declaration b. Programming Transition/Transition with Crossing bits Initialization Test on Receptivity Transition Crossing Output declaration c. Programming Step/Step d. Programming […]