PLC是按集中输入、集中输出，周期性循环扫描的方式进行工作的。它的中心工作过程分输入采样阶段、程序执行阶段、输出刷新阶段。
在输入采样阶段，首先扫描所以输入端子，并将各输入状态存入相对应的输入映像寄存器中，此时输入映像寄存器被刷新，它与外界隔离，其内容保持不变，直到下一个扫描周期的输入采样阶段。
在程序执行阶段，PLC按从左到右、从上到下的步骤顺序执行程序。
在输出刷新阶段中，元件映像寄存器中所有输出继电器的状态一起转存到输出锁存器中，通过一定方式集中输出，**后经过输出端子驱动外部负责，在下一个输出刷新阶段开始之前，输出锁存器的状态不会改变。
Siemens 6GK15024AB10 MODULE SINEC L2FO OLM/S4
Siemens 6GK15023CB10 Profibus OLM/G12
Siemens 6ES71580AD000XA?0 Profibus DP/DP Coupler
Siemens INTERFACE REMOTE I/O S7400 6ES7466-3AA00-0?XB0
Siemens 6GK15022CA00 SIMATIC NET, PB OLM/P11 V3 OPTICAL
Siemens 6ES7156-0AA01-0?XA0 DP/AS-I link
Allied Telesyn Etherenet 10Mbps RJ-45 PCI Bulk AT-2450T
ALLIED TELESYN ETHERNET ADAPTER PCI 100MBITS AT2560FX
CTI 2571 - 4 PORT EXPANDER MODULE
SIEMENS OP27 6AV36271JK000AX?0 NEW FACTORY SERVICED!!!
6AV3 627-1JK00-0AX0 NEW FACTORY SERVICED!!!
Siemens/TI 500-5035 BASIC MODULE
Siemens/TI 505-1434TF, SINEC H1 ETHERNET COM
Siemens 505-7202 FIELD INTERFACE MODULE
Siemens Simatic Net CP Profibus, CP342-5
Siemens MODULE COMM. CP342-5,NEW! 6GK73425DA020XE?0
Siemens/TI 505-CP2572 COMM-MODULE TCP IP ETHERNET
SIEMENS/TI 505-CP5434 PROFIBUS FMS COMM PROCESSOR
SIEMENS/TI 505-5184 MODBUS COMM MODULE
SIEMENS/TI 505-7201 FIELD INTERFACE MODULE
SIEMENS/TI 505-6851B REMOTE base CONTROLLER
SIEMENS/TI 505-6870 PROFIBUS- REMOTE base CONTROLLER
TI-500-5053 INTERFACE MODULE PEERlink TIWAY(NEW IN BOX)
TI-500-5039 TIWAY 1, NETWORK INTERFACE MODULE - NIM
SIEMENS/TI - 500-5114 REMOTE base, w/RS485 Port
SIEMENS/TI - 500-2109 DISTRIBUTED base CONTROLLER
SIEMENS HMI OP15-C1, CommText Firmware, Profibus
SIEMENS HMI OP5-A2 OPERATOR PANEL 6AV3505-1FB12
SIEMENS PC670 6AV7612-0AB22-0?BJ0 TOUCHSCREEN PANEL PC
SIEMENS 6AV65420BB152AX?0 OP170B OPERATOR INTERFACE
SIEMENS MP277 8 Inch Touch Panel 6AV66430CB011AX?0
SIEMENS MP277 6AV6643-0CB01-?1AX0 !!NEW IN BOX!!
IC752DSX000A GEFANUC OPERATOR PANEL, W/PROFIBUS
HE450RMU200 HORNER ELECTRIC, RMU DISPLAY W/PROFIBUS
CUTLER HAMMER PANELMATE1500 1575PM - - W/PROFIBUS
Siemens FI45 PIII-700MHZ 384MB 10GB WINNT
Siemens FI45
TCP STAINLESS STEEL BEZEL 10.5 INCH HMI-BEZ-203
TCP OPERATOR INTERFACE KEYPAD HMI-KPN-201 QUICKPANEL
Red Lion Paradigm Panel CL01 w/PAPBH Profibus module
SIEMENS HMI OP5-A1 OPERATOR PANEL 6AV3505-1FB01
SIEMENS 6AV36071JC200AX?1 OP74X40 TEXT DISPLAY
SIEMENS TP070 6AV65450AA152AX?0
SIEMENS C7634 6ES76341DF000AE?3 S7-300 CPU 315,OP17
SIEMENS OP25/A 6AV35251EA010AX?0 NEW FACTORY SERVICED!!!
6AV3 525-1EA01-0AX0 NEW FACTORY SERVICED!!!