In order to State, it is necessary to learn more about ladder diagram of common terminology.
(1) the ladder diagram
Ladder diagram of PLC program is a simple and easy to understand form. It comes from electrical schematic diagram of relay control systems, programming in schematic form the logical process of the directive, it is sometimes also known as the circuit. Because the program is shaped like a ladder, hence the name. Ladder diagram of PLC ladder diagram instructions and right-handed instructions (or Terminal instruction). Ladder diagram corresponds to the conditions on the ladder diagram, instruction is instruction, which conditions can be performed alone or in composition logic blocks, is the Foundation of all other instructions. Instruction refers to his right hand on a ladder diagram on the right, with final implementation conditions of a command in the command line.
(2) the statement list (mnemonic)
Statement form is made manifest in the order (not ladder) a form of PLC program composition. Mnemonics can provide information exactly like the ladder, but it is a form of direct type PLC. Regardless of what the programmer, programs are stored in a mnemonic form in memory. It‘s important to understanding mnemonic.
(3) conditions of normally open and normally closed
Ladder logic in the criteria can be either ON or OFF (corresponds to the power on relay or power failure), depending on the actions that you have assigned to it. If the operation is ON, normally open condition is ON; if the operation is OFF, normally open condition is a OFF. On close terms and conditions, if the operation is OFF it is ON; if the action is ON it is OFF. In General, you want to happen when a digit ON action, use normal open conditions; want action to occur when an OFF, use a normally closed conditions.
(4) implementation of conditions
In the ladder diagram programming, before an instruction ON and OFF condition the logical combination of instruction integrated conditions. This condition is either ON or OFF, known as the conditions of implementation of the directive.
IR, SR, HR, and AR, LR or any TC region, can be specified for any ladder instruction operands. This means that conditions in the ladder diagram can be I/O, flag bits, working, timer/counters, such as decisions. LD and OUT instructions TR area can also be used, but they are only used in special applications.
(6) the logical block
Correspond to the conditions and instructions, depending on the relationships between various conditions within the command line. Any set of combined, the logical outcome, known as logical block or circuit block. While preparing the ladder can do not need to analyze a single logical block, but understanding the logic blocks are necessary for effective programming; when the mnemonic input program, logical block is the Foundation.