l编程指令：指令是PLC被告知要做什么，以及怎样去做的代码或符号。从本质上讲，指令只是一些二进制代码，这点PLC与普通的计算机是完全相同的。同时PLC也有编译系统，它可以把一些文字符号或图形符号编译成机器码，所以用户看到的PLC指令一般不是机器码而是文字代码，或图形符号。常用的助记符语句用英文文字（可用多国文字）的缩写及数字代表各相应指令。常用的图形符号即梯形图，它类似于电气原理图是符号，易为电气工作人员所接受。
l指令系统：一个PLC所具有的指令的全体称为该PLC的指令系统。它包含着指令的多少，各指令都能干什么事，代表着PLC的功能和性能。一般讲，功能强、性能好的PLC，其指令系统必然丰富，所能干的事也就多。我们在编程之前必须弄清PLC的指令系统
l程序：PLC指令的有序集合，PLC运行它，可进行相应的工作，当然，这里的程序是指PLC的用户程序。用户程序一般由用户设计，PLC的厂家或代销商不提供。用语句表达的程序不大直观，可读性差，特别是较复杂的程序，更难读，所以多数程序用梯形图表达。
Mitsubishi Roithner ML701B1R-E21A 1.3um Laser Diode
Mitsubishi Roithner ML720A1S-E22E 1.3um Laser Diode
Avocent Equinox SST-4/8P Multiport Serial PCI Adapter
Automotion ALC12DE-010-131?2 Servo Amplifier Series E
Apollo Computer Excelan EXOS 302 Controller Board VME
Apollo Computer Domain Ring Board VMEbus VME
AP Tech AP1810 Pressure Regulator AP1810S-3P-660P NEW
Antec / Lightwave Communications LLMM Chassis VME
Ames 5772 Clinitek 100 Urine Chemistry Analyzer
AMCI Advanced Micro Controls Inc. DC425-1003 DuraCoder
Alliance Sys CSU DSU Adit 600 TDM Control FXS Modules
Allen Bradley SLC 500 Programmable Controller DH-485
Advance Automation Model MF2 Cylinder I-4X4-MF2-NC-1-?#2
Adtran TSU 600e Modular 1/FT1 Multiplexer PN: 1202076L1
ADC Soneplex Ver. G HLXR Module Remote HDSL Interface
ADC Soneplex Ver. D HLXR Module Remote HDSL Interface
Adaptec AHA-2740A AHA-2740A/42A/4?0AT/42AT SCSI Adapter
Acromag AVME947x / AVME9475 VMEBUS Industrial I/O Board
3Com SuperStack II 3C16610 Dual Speed 12-Port Hub 500
Panasonic CF-28 ToughBook NoteBook w/ Power Supply
TBI-Bailey ABB TBN58 pH Transmitter
Beckman JA-20 Rotor, Fixed Angle, 8 x 50mL, 20,000RPM
Beckman JA-14 Rotor, Fixed Angle, 6 x 250 mL, 14,000RPM
Beckman Spinco 152 Microfuge Centrifuge
Beckman DU-40 DU40 Spectrophotomet?er
Cincinnati Fan LM-3 Cast Aluminum Volume Blower
Dictaphone 3750 ExpressWriter Plus? w/ Headset & Foot
Baldor CDB3558T-11 Brushless DC Motor 2HP 300V 1800RPM
Central Scientific CAT#: 82489-2 Desk DC Milivolt Meter
Parker NW-04 Universal Nut Wrench 1/4” NW-04-U
Mitsubishi Roithner ML701B1R-E21A 1.3um Laser Diode
Mitsubishi Roithner ML720A1S-E22E 1.3um Laser Diode
Avocent Equinox SST-4/8P Multiport Serial PCI Adapter
Automotion ALC12DE-010-131?2 Servo Amplifier Series E
Apollo Computer Excelan EXOS 302 Controller Board VME
Apollo Computer Domain Ring Board VMEbus VME
AP Tech AP1810 Pressure Regulator AP1810S-3P-660P NEW
Antec / Lightwave Communications LLMM Chassis VME
Ames 5772 Clinitek 100 Urine Chemistry Analyzer
AMCI Advanced Micro Controls Inc. DC425-1003 DuraCoder
Alliance Sys CSU DSU Adit 600 TDM Control FXS Modules
Allen Bradley SLC 500 Programmable Controller DH-485
Advance Automation Model MF2 Cylinder I-4X4-MF2-NC-1-?#2
Adtran TSU 600e Modular 1/FT1 Multiplexer PN: 1202076L1
ADC Soneplex Ver. G HLXR Module Remote HDSL Interface
ADC Soneplex Ver. D HLXR Module Remote HDSL Interface
Adaptec AHA-2740A AHA-2740A/42A/4?0AT/42AT SCSI Adapter
Acromag AVME947x / AVME9475 VMEBUS Industrial I/O Board
3Com SuperStack II 3C16610 Dual Speed 12-Port Hub 500
Panasonic CF-28 ToughBook NoteBook w/ Power Supply
TBI-Bailey ABB TBN58 pH Transmitter
Beckman JA-20 Rotor, Fixed Angle, 8 x 50mL, 20,000RPM
Beckman JA-14 Rotor, Fixed Angle, 6 x 250 mL, 14,000RPM
Beckman Spinco 152 Microfuge Centrifuge
Beckman DU-40 DU40 Spectrophotomet?er
Cincinnati Fan LM-3 Cast Aluminum Volume Blower
Dictaphone 3750 ExpressWriter Plus? w/ Headset & Foot
Baldor CDB3558T-11 Brushless DC Motor 2HP 300V 1800RPM
Central Scientific CAT#: 82489-2 Desk DC Milivolt Meter
Parker NW-04 Universal Nut Wrench 1/4” NW-04-U
Mitsubishi Roithner ML701B1R-E21A 1.3um Laser Diode
Mitsubishi Roithner ML720A1S-E22E 1.3um Laser Diode
Avocent Equinox SST-4/8P Multiport Serial PCI Adapter
