plc除了用于开关量控制、定时、计数的基本指令外，还有大量的应用指令，有的plc的应用指令多达数百条。
对于应用指令，初学者非常困惑，不知道哪些指令重要、哪些指令常用，应该怎样学习它们。这些指令可以分为下面几种类型：
1．属于几乎所有计算机语言都有的指令，例如数据的传送、比较、移位、循环、数学运算、字逻辑运算、数据类型转换等指令。
这类指令非常重要，它们与计算机的基础知识（例如数制、数据类型、寻址方式等）有关，应通过例子和实验了解这些指令的基本功能。学好一种型号的plc的这类指令，再学别的plc的同类指令就很容易了。http://www.pw0.cn/article/plc
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Details about SIEMENS EM6B050MC1 USPP EM6B050MC1
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MITSUBISHI AACPU-S1
Details about WIX FILTERS 33394 NSFP 33394
KEYENCE ML-9100 SCANNING LASER MARKER
Details about MOOG ES2032S NSFP ES2032S
Details about WILKERSON PNEUMATIC 83-551-000 NSFP 83551000
Details about WIX FILTERS 42595 NSFP 42595
WESTINGHOUSE QP1035 USPP QP1035
Details about Rosemount Temperature sensor inThermowell 0183A-23-K2N-7-ET-228/285-A1-SB-150PT
Details about WIX FILTERS 51061 USPP 51061
DODGE 1276-00 NSFP 127600
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AMAT APPLIED MATERIALS 0010-20422 ASSY, 8 IN SHIELD TREATMENT W/PROTECTIVE USED
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Details about TAYLOR MACHINE WORKS 4044-367 NSFP 4044367
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Details about SIEMENS E3L1G NSFP E3L1G
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Details about ALLEN BRADLEY 800T-N26G NSFP 800TN26G
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SAHO// MITSUBISHI MR-J-100B AC SERVO DRIVER USED
Details about ASCO 8210G008-120/60-110/50 NSFP 8210G00812060110
Customs services and international tracking provided
WESTINGHOUSE PB1AAG USPP PB1AAG
Details about WIREMOLD 2389 NSFP 2389
Details about HONEYWELL 3800G14E USPP 3800G14E
Details about MTE RL-05512 NSFP RL05512
Details about Kielly & Mueller 1400-R Control Valve 2.5 in ANSI 300 & 36DN 155 SP284 Actuator
Details about DODGE 455115 USPP 455115
Yaskawa YASNAC JANCD-FC230B Control Card Hitachi Seiki Seicos Good Working Card
Details about SQUARE D QMB-361TW NSFP QMB361TW
WESTINGHOUSE 4D33644G03 USPP 4D33644G03
Details about PHILLIPS ECG-156 NSFP ECG156
MITSUBISHI F1-0MR-UL USPP F0MRUL
WESTINGHOUSE 1541A28G02 USPP 1541A28G02
Details about TELECT F12-SSG-M020-0 NSFP F12SSGM0200
Details about Fisher Type 98H 1"inch Stainless Pressure reducing valve PRV spring rge 25-75PSI
Details about TURCK ELEKTRONIK NI4-M12-VN6X USPP NI4M12VN6X
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Details about COMPUMOTOR AR-13CE USPP AR13CE
Details about SUN HYDRAULICS CBGALHN-HPX/S NSPP CBGALHNHPXS
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Details about WHITNEY CHAIN C2080H NSPP C2080H
Details about MITSUBISHI UA-AXV1 NSFP UAAXV1
LitbFuse JTD10 Time Delay Current Limiting 10 Amp Fuse
Details about SIEMENS 6SE6-400-0BE00-0AA0 USPP 6SE64000BE000AA0
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SICK OPTIC ELECTRONIC KD5-SYF830 NSPP KD5SYF830
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Details about KING ENGINEERING 7859-2 NSPP 78592
Details about NATIONAL SEMICONDUCTOR NM93C56N FNFP NM93C56N
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Details about LANDIS & GYR GDE163.1P NSFP GDE1631P
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Details about P&H MINING EQUIPMENT 79U6D4 NSPP 79U6D4
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Details about SIEMENS 6GT2091-1CH20 FNFP 6GT20911CH20
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Details about Yokogawa EJX530A S2 DBS4N-014EF/SU2/X2 Pressure Transmitter
RELIANCE ELECTRIC 45C-401 USPP 45C401
Details about WAGNER PRODUCTS H6054 NSFP H6054
Details about NATIONAL SEMICONDUCTOR IC9602N FNFP IC9602N
RELIANCE ELECTRIC 0-49017-80 USPP 04901780
Details about YALE 580012294 NSFP 580012294
Details about ALLEN BRADLEY 592-A2GA USPP 592A2GA
Details about FESTO ELECTRIC CPV10-M1H-5LS-M7 NSFP CPV10M1H5LSM7
Details about DORMAN 80583 NSFP 80583
WESTINGHOUSE 966481-H USPP 966481H
 
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WESTINGHOUSE 212P106H01B USPP 212P106H01B
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Details about JOMAR T-100/ST-1-1/4 NSPP T100ST114
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Details about Baugh and Weeden Type 1015 Ultrasonic NDT flaw detector
Details about CNH INDUSTRIAL 83417133 FNFP 83417133
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HMK-3993-04 Yaskawa / Yasnac CNC Keyboard TESTED
Details about Engineering Metrology Comparator Probe
RELIANCE ELECTRIC P18G3338-G USPP P18G3338G
DODGE 40BTL19H-1210 NSPP 40BTL19H1210
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Details about SIEMENS 6FC5-357-0BB23-0AE0 USPP 6FC53570BB230AE0
Details about FERRAZ SHAWMUT NDMM NSFP NDMM
WESTINGHOUSE BAB2035 NSFP BAB2035
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DODGE 023384 NSFP 023384
Omron CJ1W-NC233 CJ1WNC233 2 AXES POSITION CONTROL UNIT
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MAN ROLAND AV000
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RELIANCE ELECTRIC 45C-46 NSFP 45C46
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Details about ITE SIEMENS ED41B050 USPP ED41B050
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Allen Bradley 1336-B005-EAD-S1 VFD 5Hp 380-460 Vac AC Speed Control
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DODGE 006752 NSFP 006752
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SERVOPACK CPCR-MR 053 G CPCR-MR 053 G 

2．与顺序控制程序有关的指令。这类指令中，fx的stl指令设计得最好，用stl指令设计的梯形图与顺序功能图之间有明确的对应关系，因此易于理解和使用，设计的程序比其他方法设计的短，可以节约大量的设计时间。
s7-200的scr（顺序控制继电器）指令和欧姆龙的步指令（step/snxt）也用于编写顺序控制程序。
建议在学习这类指令之前，首先学习顺序功能图（见作者编写的plc教材）。
3．与plc的高级应用有关的指令，例如与pid控制、运动控制、高速输入/高速输出、通信有关的指令，这些指令也很重要。某些指令需要学习有关的专门知识，才能正确的理解和使用它们。
4．与plc特定的硬件、软件有关的指令，例如读写特殊模块和模拟电位器的指令，s7-300/400读取数据块长度和编号的指令等。
5．与某些特定的工程应用有关的指令。例如fx的凸轮顺控指令和旋转工作台控制指令。
学习应用指令时，可以首先按指令的分类浏览所学的plc有哪些应用指令，它们用来干什么，便于在需要的时候能找到手册或帮助中的指令说明。初学时没有必要花大量的时间去了解应用指令的详细使用方法，更没有必要去死记硬背它们。重点是了解指令的基本功能。
可以采用需要什么学什么的方法，重点学习读程序、编程序时遇到的和需要使用的指令，没有用到的指令暂时不管它。在阅读或编写程序时如果遇到不常用的指令，可以通过编程手册了解它们的详细使用方法。
如果编程软件有指令的在线帮助，选中指令列表或程序中的某条指令，按一下f1键，就可以看到该指令的大量细节，例如指令各参数的数据类型、可用的存储区、参数的意义，指令的功能和应用实例、指令的执行对状态字或有关标志位的影响等。
与学外语不能只靠背单词，应主要通过阅读和会话来学习一样，要学好plc的应用指令，也离不开实践。一定要在读程序和编程序的过程中学习应用指令。
有的指令实际上极少使用，它们属于“休眠”的指令，学习的时候可以不管它们。万一在读程序时遇到它们，可以通过指令的在线帮助或查手册来了解它们。

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