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为此，PLC的工作速度要快。速度快、执行指令时间短，是PLC实现控制的基础。事实上，它的速度是很快的，执行一条指令，多的几微秒、几十微秒，少的才零点几，或零点零几微秒。而且这个速度还在不断提高中。
图1－1－1所示的过程是简化的过程，实际的 PLC工作过程还要复杂些。除了 I/O刷新及运行用户程序，还要做些公共处理工作。
公共处理工作有：循环时间监控、外设服务及通讯处理等。
监控循环时间的目的是避免"死循环"，避免程序不能反复不断地重复执行。办法是用""（Watching dog）。只要循环**时，它可报警，或作相应处理.

MOTOROLA MVME050 SYS CONTROLLER VME MODULE
MOTOROLA MVME-050 USPP MVME050
MOTOROLA MVME0642-350 CPU W/4MB VME MODULE
MOTOROLA MVME0642-350 CPU W/4MB VME MODULE
MOTOROLA MVME110 VME BUS MAIN FRAME BOARD CPU SLAVE BOARD B104
Motorola MVME110-1 AMAT 0100-11018
MOTOROLA MVME-110-1 USPP MVME1101
MOTOROLA MVME117-4 VMEBUS 12.5MHZ MC68010 PROCESSOR 512KB OF DUAL PORTED
MOTOROLA MVME123 VMEBUS 12.5MHZ MC68010 PROCESSOR 512KB OF DUAL PORTED DYNAMIC
MOTOROLA MVME1301 01-W3108F MPC603 66 Mhz, 8MB DRAM
MOTOROLA MVME1301 MPC603 66MHZ CPU W/8MB DRAM
MOTOROLA MVME133 CPU W/1MB VME MC68020 CPU 125MHZ
MOTOROLA MVME133 CPU W/1MB VME MC68020 CPU 125MHZ
Motorola MVME133A-20 VMEmodule User's Manual
Motorola MVME133XT Controller Board Rev. A  WOW
MOTOROLA MVME-133XT VME CIRCUIT BOARD
MOTOROLA MVME-133XT VME CIRCUIT BOARD
MOTOROLA MVME133XT VMEmodule USER'S MANUAL
MOTOROLA MVME-143S-2 USPP MVME143S2
MOTOROLA MVME147  CPU MODULE 01-W3347F-43A 16 MEG
Motorola MVME147 64-W5401C02A Rev B
Motorola MVME147 64-W5892B01B rev. B
Motorola MVME-147-011 Ethernet SCSI Card 25mhz 109a-ak
MOTOROLA MVME-147-011 USPP MVME147011
Motorola MVME147-022 MVME 147-022 Module PN 01-W3964B
MOTOROLA MVME-147-023 USPP MVME14702
MOTOROLA MVME-147SB-1 USPP MVME147SB1
MOTOROLA MVME-147SB-2 USPP MVME147SB2
MOTOROLA MVME-147SC-2 USPP MVME147SC2
MOTOROLA MVME147SC-2 VME 68030 CPU 33MHZ 32MB MEMORY
MOTOROLA MVME147SC-2 VME 68030 CPU 33MHZ 32MB MEMORY
MOTOROLA MVME147SRF MVME-147SRF CPU BOARD
MOTOROLA MVME-147SRF NSFP MVME147SRF
Motorola MVME1600-011 MVME1603 / MVME1604 BRAND
MOTOROLA MVME1600-011 MVME1604 POWERPC 604 PM604 CPU / MEMORY MODULE ONBOARD
MOTOROLA MVME1603/MVME1604 Single Board Computer
MOTOROLA MVME1603-053 MVME1600-011 POWER PC 200MHZ CPU WITH 16MB MEMORY
MOTOROLA MVME1604-023 USPP MVME1604023
Motorola MVME-162-01 Embedded Controller
MOTOROLA MVME162-010 MC68LC40 CPU 25MHZ 4MB MEMORY 512K
Motorola MVME162-013A Module With MVME712/M and Accessories
MOTOROLA MVME-162-020A USPP MVME162020A
MOTOROLA MVME162-032 01-W3884B W/ LAN PORTS ADD ON BORD 30 DAY WARRANTY
Motorola MVME-162-201 PLC Controller Module  WOW
Motorola MVME-162-220 PLC Controller Module  WOW
MOTOROLA MVME162-222 68040 CPU 25MHZ 4MB MEMORY 512K
MOTOROLA MVME162-223 68040 CPU, 25MHZ, 4MB MEMORY, 512K SDRAM, 4 IP PORTS
MOTOROLA MVME162-412 68040 CPU, 25MHZ, 16MB DRAM MEMORY, 128KB SRAM, 1MB FLASH
MOTOROLA MVME162-413 68040 CPU, 25MHZ,16MB DRAM MEMORY,128KB SRAM, 1MB FLASH
MOTOROLA MVME162-432 01-W3960B MVME 162-432    30 DAY WARRANTY
MOTOROLA MVME162-432 68040 CPU, 25MHZ, 8MB DRAM MEMORY,128KB SRAM, 1MB FLASH MEM
MOTOROLA MVME162-510A
MOTOROLA MVME-162-510A USPP MVME162510A
Motorola MVME162-522A CPU Processor SBC VME Board 162
Motorola MVME162-522A CPU Processor SBC VME Board 162
MOTOROLA MVME162-522A VME BOARD 01-W3960B MVME 162-522A
MOTOROLA MVME162-522A VME BOARD 01-W3960B MVME 162-522A
Motorola MVME162-523 MVME 162-523 CPU Board
Motorola MVME162-533A CPU Board
Motorola MVME162FX Installation Users Manual
MOTOROLA MVME165-03 68040 CPU, 33MHZ, 4MB MEMORY, VSB, 2 SERIAL PORTS, A32/D32
MOTOROLA MVME165A 68040 CPU, 25MHZ, 16MB MEMORY MODULE
Motorola MVME166-011A 01-W3179F01A
MOTOROLA MVME166-012A 68040 CPU, 33MHZ WITH 8MB ECC MEMORY, BATTERY BACKUP, LAN,
Motorola MVME167 Installation Guide
Motorola MVME-167 MVME167 Single Board Module VME
Motorola MVME-167 MVME167 Single Board Module VME
MOTOROLA MVME-167 USPP MVME167
MOTOROLA MVME167-01A USPP MVME16701A
MOTOROLA MVME-167-01B USPP MVME16701B
Motorola MVME167-02B MVME 167-02B Single Board VME
Motorola MVME167-02B MVME 167-02B Single Board VME
MOTOROLA MVME167-031A 68040 CPU, 33MHZ WITH 4MB PARITY MEMORY, 1 LAN INTERFACE
MOTOROLA MVME167-03B W3690B 03F CPU 25MHZ W3899B 38C
MOTOROLA MVME167-04B NSPP MVME16704B
Motorola MVME167-33B CPU Processor VME Board
Motorola MVME167-33B CPU Processor VME Board
Motorola MVME167-34B
Motorola MVME167-34B VME MVME SBC
Motorola MVME167-34B VME MVME SBC
Motorola MVME177-004
Motorola MVME177-004
Motorola MVME177-004 6060-0015
Motorola MVME181-1 MVME 181-1 VME Module
Motorola MVME181-1 MVME 181-1 VME Module
Motorola MVME187 MVME 187 VME Module
Motorola MVME187 MVME 187 VME Module
MOTOROLA MVME187 USPP MVME187
Motorola MVME197LE 01-W3091F MVME 197LE
Motorola MVME197LE Single Board Computer Module VME
Motorola MVME197LE Single Board Computer Module VME
Motorola MVME202 MVME-202 Mainframe Board VME
Motorola MVME202 MVME-202 Mainframe Board VME
MOTOROLA MVME-204-2F USPP MVME2042F
MOTOROLA MVME-204A728-1 USPP MVME204A7281
Motorola MVME211 RAM / ROM / EPROM VME Memory Module
Motorola MVME211 RAM / ROM / EPROM VME Memory Module
MOTOROLA MVME215-1 256Kb/1Mb STAT RAM MEMORY MODULE
MOTOROLA MVME215-2 NSPP MVME2152
Motorola MVME222-1 MVME 222-1 VME Mainframe Board VME
Motorola MVME222-1 MVME 222-1 VME Mainframe Board VME
Motorola MVME-224A-1 MVME224A-1 VME Mainframe Board
Motorola MVME-224A-1 MVME224A-1 VME Mainframe Board
MOTOROLA MVME-225-2 USPP MVME2252
Motorola MVME2304 CPU Processor SBC VME Board SBS PMC-3101
Motorola MVME2304 CPU Processor SBC VME Board SBS PMC-3101
Motorola MVME2304 MV2304-0123VX Controller with 60 day warranty
Motorola MVME2306 01-W3345F-26A 300mhz MPC604 32mb RAM  MVME-2306
Motorola MVME2306 CPU Processor SBC VME Board ADM-XRC Virtex PMC
Motorola MVME2306 CPU Processor SBC VME Board ADM-XRC Virtex PMC
Motorola MVME2306 MV2306VX Controller with 60 day warranty
Motorola MVME-2307 SBC VME Module PCI Mezzanine Carrier
Motorola MVME-2307 SBC VME Module PCI Mezzanine Carrier
MOTOROLA MVME-236-2
Motorola MVME236-2 MVME-236-2 VMEbus DRAM Memory Module
MOTOROLA MVME2400 MV2400 XLT Fast shipping
Motorola MVME2434-1 mvme 2434 2400 Series VME
Motorola MVME2434-1 mvme 2434 2400 Series VME
MOTOROLA MVME2600-2 MVME 2600 VME BUS CARD MODULE MAINFRAME CPU BOARD PROCESSOR
MOTOROLA MVME2600-2 MVME 2600 VME BUS CARD MODULE MAINFRAME CPU BOARD PROCESSOR
MOTOROLA MVME2603 2603 712 I/O VME BUS CARD MODULE MAINFRAME PROCESSOR 160975-01
MOTOROLA MVME2603 2603 712 I/O VME BUS CARD MODULE MAINFRAME PROCESSOR 160975-01
MOTOROLA MVME2603 761 I/O PCI MEZZANINE CARD TPMC815 #A
Motorola MVME2603 MVME-2603 VME Mainframe Processor
Motorola MVME2603 MVME-2603 VME Mainframe Processor
Motorola MVME2604 761 I/O VME CPU Board, MVME SBC
Motorola MVME2604 761 I/O VME CPU Board, MVME SBC
MOTOROLA MVME2604 761 I/O VME CPU Power PC Board
MOTOROLA MVME2604 761 I/O VME CPU Power PC Board
MOTOROLA MVME2700-761-I/O USPP MVME2700761IO
MOTOROLA MVME-300A
Motorola MVME-316 VME VMEbus-I/O CH Interface Board
Motorola MVME-316 VME VMEbus-I/O CH Interface Board
MOTOROLA MVME320B-1 USPP MVME320B1
Motorola MVME328-1 MVME 328-1 SCSI VME Board
Motorola MVME328-1 MVME 328-1 SCSI VME Board
MOTOROLA MVME331 USPP MVME331
MOTOROLA MVME332XT 8 CHANNEL CONTROLLER MODULE -
MOTOROLA MVME-332XT USPP MVME332XT
Motorola MVME332XTP MVME 332XTP VME Board
Motorola MVME332XTP MVME 332XTP VME Board
MOTOROLA MVME332XTS 8-CHANNEL CONTROLLER VME MODULE
MOTOROLA MVME332XTS 8-CHANNEL CONTROLLER VME MODULE
MOTOROLA MVME333S-2 8-CHANNEL CONTROLLER VME MODULE
MOTOROLA MVME333S-2 8-CHANNEL CONTROLLER VME MODULE
Motorola MVME333S-2 Mainframe Board VME 01-W3775B, Communications O56
Motorola MVME333S-2 Mainframe Board VME 01-W3775B, Communications O56
Motorola MVME337-1 MVME 337-1 VME Module
Motorola MVME337-1 MVME 337-1 VME Module
Motorola MVME339 MVME-339 VME Control Board
Motorola MVME339 MVME-339 VME Control Board
MOTOROLA MVME-340 USPP MVME340
Motorola MVME340A Parallel Interface Timer Module
MOTOROLA MVME-340A USPP MVME340A
MOTOROLA MVME-350 USPP MVME350
Motorola MVME374-1 MVME 374-1 VME Module
Motorola MVME374-1 MVME 374-1 VME Module
MOTOROLA MVME-376 USPP MVME376
Motorola MVME-376 VME Ethernet Control Board
Motorola MVME-376 VME Ethernet Control Board
Motorola MVME-376 VME Ethernet Control Board