1：根据工程实际需求，进行功能块规划，编写子程序
在PLC中，子程序是为一些特定的控制目的编制的相对独立的程序。执行子程序调用指令CALL等，如果条件不满足子程序调用时，程序的扫描就仅在主程序中进行，不再去扫描这段子程序，这样就减少了不必要的扫描时间。
2：用字或双字数据传送给DO点方法来控制输出
在PLC的应用中通常都会有大量的输出控制，用字或双字数据传送给DO点方法来控制输出可以提高速度，只要根据实际应用的要求，合理分配输出地址，变换控制输出控制字，可以大大减少PLC程序执行的步数，从而加快PLC的程序运行速度。
3：脉冲触发SET、RESET
PLC中，使用SET指令只执行一次即可，不必每次扫描都执行这个指令，很适合与脉冲输出(PLS/PLF)指令配合使用。有些工程人员忽视了这个问题，使用了常规的方法来驱动SET指令，无意中增加了PLC程序扫描运行时间
4：避免了类型转换，方法如下：
以S7-200为例，它的内存格式与我们常用的PC机正好相反，它是高字在前，低字在后的。所以我们可以将字变量放在后两个字节，在程序初始化时将前两个字节清零(程序的其它地方不得使用这两个字节)。
如我们定义符号时将字变量定义在VW2，同时保持VW0的值为零。则程序中可以用VW2以字型访问该变量，同时也可以VD0以双字型访问，避免了类型转换。
为了避免使用时混淆，以明确的符号定义来区分字类型和双字类型。在此强烈推荐类匈牙利命名法：以前缀指示变量类型，用首字母大写的有意义的英文单词的组合作变量名本人习惯用以下缀：
b----字节型变量(byte)
w----字型变量(word)
d----双字变量(double)
r----实型变量(real)
f----位变量(flag)
btn---自复位按钮式输入(button)
sw----切换开关或自锁按钮输入(switch)
sig---传感器、编码等电平信号输入(signal)
rly---输出继电器位(relay)
How to improve the running speed of PLC program can adopt the following programming methods for reference only:1: According to the actual needs of the project, plan the function block and write the subroutine
In PLC, subroutine is a relatively independent program compiled for some specific control purposes. Execute the subroutine call instruction call, etc. if the conditions do not meet the subroutine call, the program scanning is only carried out in the main program, and this subroutine is no longer scanned, which reduces the unnecessary scanning time.
2: The output is controlled by the method of transmitting word or double word data to do point
In the application of PLC, there are usually a large number of output controls. The method of transmitting word or double word data to do point can improve the speed. As long as the output address is reasonably allocated and the control output control word is changed according to the requirements of practical application, the steps of PLC program execution can be greatly reduced, so as to speed up the running speed of PLC program.
3: Pulse trigger set, reset
In PLC, the set instruction can be executed only once. It is not necessary to execute this instruction every time. It is very suitable for use with pulse output (PLS / PLF) instruction. Some engineers ignore this problem and use conventional methods to drive set instructions, which inadvertently increases the scanning running time of PLC program
4: Type conversion is avoided as follows:
Taking S7-200 as an example, its memory format is just opposite to that of our commonly used PC. It is high word first and low word last. Therefore, we can put the word variable in the last two bytes and clear the first two bytes during program initialization (these two bytes shall not be used elsewhere in the program).
For example, when defining symbols, we define the word variable in vw2 and keep the value of vw0 zero. In the program, you can use vw2 to access the variable in font, and VD0 can also be accessed in double font, avoiding type conversion.
In order to avoid confusion in use, clear symbol definitions are used to distinguish word types and double word types. Hungarian like nomenclature is strongly recommended here: the prefix indicates the type of variable, and the combination of meaningful English words with uppercase letters is used as the variable name. I am used to using the following suffix:
B --- byte type variable (byte)
W --- font variable (word)
D --- double variable
R ---- real variable (real)
F --- bit variable (flag)
BTN --- self reset button input
SW ---- switch or self-locking button input (switch)
SIG --- sensor, coding and other level signal input (signal)
Rly --- output relay bit (relay)
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