PLC programming language and programming skills

ladder diagram programming language in the form of ladder diagram with relay control circuit, it is commonly used in the electric control system of relay, contactor logic control based on simplified evolved symbol, image, intuitive, practical.

ladder diagram design should pay attention to the following three points:

A) Ladder diagram from left to right, from top to bottom of the order. Each logical line starts at the left bus bar, and then is contact list, and connection, the last is the coil is combined with the right bus.

( 2) Each step in the ladder diagram flow is not a physical current, but the concept of 'current', from left to right, its both ends there is no power supply. The concept of 'current' is vividly described in the user program execution coil connected to meet the conditions.

( 3) Input relay is used to receive the external input signal, but not by PLC controller internal other relay contacts to drive. Therefore, ladder diagram only appear in the input relay contact, but not in the coil. Output relay output program execution results to the external output device, when the ladder diagram of the output relay coil to electricity, signal output, but not direct drive output devices, and to go through the relay output interface, transistors or thyristor can be achieved. The output relay contacts for internal use. Programming language statements table

command statement said a similar mnemonics to computer assembly language programming, but better than assembly language easy to learn. An instruction statement by step sequence, instruction and the function device Numbers of three parts. Flow chart of control system programming diagram

flow chart of control system is a relatively new programming method. It is like a flow chart of control system of the functional diagram express a process control, the current international electrotechnical society ( IEC） Ongoing development of this new programming standards.

二、基本指令简介

基本指令如表所示

取指令

LD

I、Q、M、SM、T、C、V、S、L

常开接点逻辑运算起始

取反指令

LDN

I、Q、M、SM、T、C、V、S、L

常闭接点逻辑运算起始

线圈驱动指令

Q、M、SM、T、C、V、S、L

驱动线圈的输出 与指令

I、Q、M、SM、T、C、V、S、L

单个常开接点的串联

与非指令

AN

I、Q、M、SM、T、C、V、S、L

单个常闭接点的串联

或指令

I、Q、M、SM、T、C、V、S、L

单个常开接点的并联

或非指令

ON

I、Q、M、SM、T、C、V、S、L

单个常闭接点的并联

置位指令

I、Q、M、SM、T、C、V、S、L

使动作保持

复位指令

I、Q、M、SM、T、C、V、S、L

使保持复位

正跳变

ED

I、Q、M、SM、T、C、V、S、L

输入信号上升沿产生脉冲输出

负跳变

EU

I、Q、M、SM、T、C、V、S、L

输入信号下降沿产生脉冲输出

空操作指令

NOP 无

三、使步序作空操作

1、标准触点 LD、A、O、LDN、AN、ON、

LD，取指令。 Said a normally open contacts are connected to the input bus commands, namely the normally open contacts logic operation.

LDN, take the instructions. Said a normally closed contacts are connected to the input bus commands, namely the normally closed contact logic operation.

A, and instructions. For a single series of normally open contacts. The AN, with the instructions. For a single series of normally closed contacts.

O, or instructions. Used for parallel single normally open contacts. ON, or the instructions. Used for parallel single normally closed contacts.

2, positive and negative jump ED, EU

ED, when it detects a positive jump ( From OFF to ON) Later, can let flow through to a scan cycle.

EU, detects a negative jump ( From ON to OFF) Later, can let flow through to a scan cycle.

=

= 3, output, when to execute commands output, specify the parameters on the image to register is connected.

4, setting and reset instruction S, R

S, perform setting ( Buy 1) Instructions, starting from the bit or OUT the address specified parameters of N points have been setting.

R, execute reset ( S) Instructions, starting from the bit or OUT the address specified parameters of N points have been reset.

setting and points can be 1 to reset 255, when use reset instruction, if the bit or OUT are specified by the T/C, so the timer or counter are reset, and the current value will be reset.

5, nops instruction NOP

the NOP instruction does not affect the execution of the program, the number of executions N ( 1 - 255). 。 The arrangement of the contact

ladder diagram of contact should draw on the horizon, can't draw on the vertical branch. Series and parallel processing

when there are several series circuit in parallel, should the series circuit will contact most on the top ladder diagram. When several parallel circuits that series, contact should be the most parallel circuits on the ladder diagram of the left. The arrangement of the coil

can't touch by drawing on the right side coil, can only receive coil on the right side of the contact. No double coil output

if the coils of the same element in the same program using two or more times, it is called a double coil output. The previous output is invalid at this moment, only the last time is valid, so should not appear double coil output. Reorganized circuit

if the circuit structure is more complex, reusable some touch point out its equivalent circuit, then program is relatively easy. Programming suitable

sequence of complex procedures can be put into a few simple procedures section, and each paragraph from the contact on the left, then by programming in comparison to the right, then connect the program segment.

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