系统程序是PLC赖以工作的基础，采用汇编语言编写，在PLC出厂时就已固化于ROM型系统程序存储器中。
系统程序分为系统监控程序和解释程序。
系统监控程序用于监视并控制PLC的工作，如诊断PLC系统工作是否正常，对PLC各模块的工作进行控制，与处设交换信息，根据用户的设定使PLC比处在编制用户程序状态或者处在运行用户程序状态等。
解释程序用于把用户程序解释成微处理器能够执行的程序。来自PLC之家
编程器是PLC的最重要外围设备。利用编程器将用户程序送入PLC的存储器
Emerson Delta V KJ4001X1-NA1 Dual Right Extender Rev. C BCK
Allen Bradley 170946 SPK Drive Control Board 170945 Rev.04, DSQ
Siemens 6GK1 500-3AA10 Optical Bus Terminal Simatic Net 6GK15003AA10, CSQ
GEC ALSTHOM PARVEX MC23SR005 SERVO MOTOR 3000 RPM 2.2/3.3 KW V
ABB KT3MIF2 Mechanical Interlock NIOB GRO
Allen Bradley 1336-PB-SP3C, 1336 SPK Drive Board, Rev 01, DSQ
Honeywell Rev. C Measurex Backplane Assembly BIC5
Mitsubishi A1S68DAI D/A Converter Unit 4-20mA CSQ
Allen Bradley 120659 148363 SPK Control Board with Display 120663 120712 CSQ
Mean Well SD-50B-5 24 VDC 3A 10A in Open Box CSQ
Reliance Electric 57C404C Network Communications Module BCK
Allen Bradley 1336T-GT1-SP51A SPK PC Board 1336T-LM1EN51 MISSING CONNECTOR CSQ
Festo 377064 NIB Bowl Assembly CSQ
Caterpillar RS-232C Communication Module CSQ SNC
Horiba HP-480 pH Meter Advanced Techno VAC, 10VA, 50/60Hz CSQ
Reliance Electric 45C410A Automate 40 Control Processor CSQ
Omron E5C4-R20J999K Temperature Controller NOS CSQ
Allen Bradley A06 Spare Drive Board Power Flex 700 150HP CSQ
Square D Combination Starter 8539SDA13V81ACFF4G20G26H30P42P46TX22 Size 2 45Amp
Siemens 6ES7 132-4BB01-0AB0 Electron Module, Simatic S7, 6ES71324BB010AB0, CSQ
Admag AM11-DEA1A-000, Magnetic Flow Converter, Yokogwa, AM11DEA1A000, CSQ
Reliance Electric 45C410A Automate 40 Control Processor CSQ
Allen Bradley Power Flex DC Control Board MMC
Cutler Hammer 8161B-1X2 60 Series Photoelectric Controller 90-132 VAC BCK
LXE 4400L20 Transceiver 2280 Terminal 1 Watt CSQ
Bridgeport Textron EAF Control Board R2E4 CSQ
Yokogawa YEW Analog Digital Display 4-20 mADC NIOB MMC
Omron CS1W-CRM21 CS1WCRM21 Remote Master Unit CSQ
Westinghouse 235P490H01 Input Module BCK
Schneider Automation 140XBP00600 6Slot Backplane Module CSQ
Signal Division Bell Mechanism Series A1 120VAC Gray NOS CSQ
Foxboro P0400ZG-0A Nodebus Interface GPP
Allen Bradley 1585J-M8CBJM-0M3 Ethernet Patchcord Shielded in Bag BCK
GE A16B Input Module 16 Point , CSQ
Beckhoff Stepper Motor AS AS1060 0000 CSQ
Schneider Electric LAD7B10 Terminal Block CSQ
Allen Bradley 1492-IFM40F LOT of Six Interface Modules BIC5
Allen Bradley 1336T-GT1-SP51A SPK Drive Board with 1336T-LM1EN CSQ
