1、數(shù)據(jù)緩沖

由于I/O設(shè)備的速率較低而CPU和內(nèi)存的速率卻很高，故在控制器中必須設(shè)置一緩沖器。在輸出時(shí)，用此緩沖器暫存由主機(jī)高速傳來的數(shù)據(jù)，然后才以I/O設(shè)備所具有的速率將緩沖器中的數(shù)據(jù)傳送給I/O設(shè)備；在輸入時(shí)，緩沖器則用于暫存從I/O設(shè)備送來的數(shù)據(jù)，待接收到一批數(shù)據(jù)后，再將緩沖器中的數(shù)據(jù)高速地傳送給主機(jī)。

2、差錯(cuò)控制

設(shè)備控制器還兼管對由I/O設(shè)備傳送來的數(shù)據(jù)進(jìn)行差錯(cuò)檢測。若發(fā)現(xiàn)傳送中出現(xiàn)了錯(cuò)誤，通常是將差錯(cuò)檢測碼置位，并向CPU報(bào)告，于是CPU將本次傳送來的數(shù)據(jù)作廢，并重新進(jìn)行一次傳送。這樣便可保證數(shù)據(jù)輸入的正確性。

3、數(shù)據(jù)交換

這是指實(shí)現(xiàn)CPU與控制器之間、控制器與設(shè)備之間的數(shù)據(jù)交換。對于前者，是通過數(shù)據(jù)總線，由CPU并行地把數(shù)據(jù)寫入控制器，或從控制器中并行地讀出數(shù)據(jù)；對于后者，是設(shè)備將數(shù)據(jù)輸入到控制器，或從控制器傳送給設(shè)備。為此，在控制器中須設(shè)置數(shù)據(jù)寄存器。

4、狀態(tài)說明

標(biāo)識和報(bào)告設(shè)備的狀態(tài)控制器應(yīng)記下設(shè)備的狀態(tài)供CPU了解。例如，僅當(dāng)該設(shè)備處于發(fā)送就緒狀態(tài)時(shí)，CPU才能啟動(dòng)控制器從設(shè)備中讀出數(shù)據(jù)。為此，在控制器中應(yīng)設(shè)置一狀態(tài)寄存器，用其中的每一位來反映設(shè)備的某一種狀態(tài)。當(dāng)CPU將該寄存器的內(nèi)容讀入后，便可了解該設(shè)備的狀態(tài)。

5、接收和識別命令

CPU可以向控制器發(fā)送多種不同的命令，設(shè)備控制器應(yīng)能接收并識別這些命令。為此，在控制器中應(yīng)具有相應(yīng)的控制寄存器，用來存放接收的命令和參數(shù)，并對所接收的命令進(jìn)行譯碼。例如，磁盤控制器可以接收CPU發(fā)來的Read、Write、Format等15條不同的命令，而且有些命令還帶有參數(shù)；相應(yīng)地，在磁盤控制器中有多個(gè)寄存器和命令譯碼器等。

6、地址識別

就像內(nèi)存中的每一個(gè)單元都有一個(gè)地址一樣，系統(tǒng)中的每一個(gè)設(shè)備也都有一個(gè)地址，而設(shè)備控制器又必須能夠識別它所控制的每個(gè)設(shè)備的地址。此外，為使CPU能向（或從）寄存器中寫入（或讀出）數(shù)據(jù)，這些寄存器都應(yīng)具有唯一的地址。

ABB GFD233A

ABB發(fā)明、制造了眾多產(chǎn)品和技術(shù)，其中包括全球第一套三相輸電系統(tǒng)、世界上第一臺自冷式變壓器、高壓直流輸電技術(shù)和第一臺電動(dòng)工業(yè)機(jī)器人，并率先將它們投入商業(yè)應(yīng)用。ABB擁有廣泛的產(chǎn)品線，包括全系列電力變壓器和配電變壓器，高、中、低壓開關(guān)柜產(chǎn)品，交流和直流輸配電系統(tǒng)，電力自動(dòng)化系統(tǒng)，各種測量設(shè)備和傳感器，實(shí)時(shí)控制和優(yōu)化系統(tǒng)，機(jī)器人軟硬件和仿真系統(tǒng)，高效節(jié)能的電機(jī)和傳動(dòng)系統(tǒng)，電力質(zhì)量、轉(zhuǎn)換和同步系統(tǒng)，保護(hù)電力系統(tǒng)安全的熔斷和開關(guān)設(shè)備。這些產(chǎn)品已廣泛應(yīng)用于工業(yè)、商業(yè)、電力和公共事業(yè)中。

ABB集團(tuán)位列全球500強(qiáng)企業(yè)（2008年在世界500強(qiáng)排列第256位，2009年位列第230位，2010年位列第237位），2009至2011年銷售額都高達(dá)320億美元。并在蘇黎世、斯德哥爾摩和紐約證券交易所上市交易。

安全回路是保護(hù)負(fù)載或控制對象以及防止操作錯(cuò)誤或控制失敗而進(jìn)行連鎖控制的回路。在直接控制負(fù)載的同時(shí)，安全保護(hù)回路還給PLC輸入信號，以便于PLC進(jìn)行保護(hù)處理。安全回路一般考慮以下幾個(gè)方面。

（1）短路保護(hù)應(yīng)該在PLC外部輸出回路中裝上熔斷器，進(jìn)行短路保護(hù)。最好在每個(gè)負(fù)載的回路中都裝上熔斷器。

（2）互鎖與聯(lián)鎖措施除在程序中保證電路的互鎖關(guān)系，PLC外部接線中還應(yīng)該采取硬件的互鎖措施，以確保系統(tǒng)安全可靠地運(yùn)行。

（3）失壓保護(hù)與緊急停車措施PLC外部負(fù)載的供電線路應(yīng)具有失壓保護(hù)措施，當(dāng)臨時(shí)停電再恢復(fù)供電時(shí)，不按下“啟動(dòng)”按鈕PLC的外部負(fù)載就不能自行啟動(dòng)。這種接線方法的另一個(gè)作用是，當(dāng)特殊情況下需要緊急停機(jī)時(shí)，按下“急?！卑粹o就可以切斷負(fù)載電源，同時(shí)“急停”信號輸入PLC。

（4）極限保護(hù)在有些如提升機(jī)類超過限位就有可能產(chǎn)生危險(xiǎn)的情況下，設(shè)置極限保護(hù)，當(dāng)極限保護(hù)動(dòng)作時(shí)直接切斷負(fù)載電源，同時(shí)將信號輸入

ABB GFD233A

1. Data buffering

Because the I/O device speed is low and the CPU and memory speed is high, a buffer must be set in the controller. When output, the buffer is used to temporarily store the data from the host at high speed, and then the data in the buffer is transmitted to the I/O device at the rate that the I/O device has; During input, the buffer is used to temporarily store the data sent from the I/O device, and after receiving a batch of data, the data in the buffer is transmitted to the host at high speed.

2. Error control

The device controller is also responsible for error detection of data transmitted by the I/O device. If an error is found in the transmission, the error detection code is usually set and reported to the CPU, so the CPU will cancel the data sent this time and retry the transmission. This ensures the correctness of data input.

3. Data exchange

This refers to the realization of data exchange between the CPU and the controller, and between the controller and the device. For the former, through the data bus, the CPU writes the data to the controller in parallel, or reads the data from the controller in parallel; In the latter case, the device inputs data to the controller, or from the controller to the device. For this purpose, a data register must be set up in the controller.

4. Status description

Identifying and reporting the status of the device The controller should record the status of the device for the CPU to understand. For example, the CPU can start the controller to read data from the device only when the device is in the send-ready state. To this end, a status register should be set up in the controller, and each bit of it reflects a certain state of the device. When the CPU reads the contents of the register, it can learn the state of the device.

5. Receive and recognize commands

The CPU can send many different commands to the controller, and the device controller should be able to receive and recognize these commands. Therefore, there should be a corresponding control register in the controller, which is used to store the received commands and parameters, and to decode the received commands. For example, the disk controller can receive 15 different commands from the CPU, such as Read, Write, Format, etc., and some commands have parameters; Accordingly, there are multiple registers and command decoders in the disk controller.

6. Address recognition

Just as every unit in memory has an address, every device in the system has an address, and the device controller must be able to recognize the address of every device it controls. In addition, in order for the CPU to write (or read) data to (or from) registers, these registers should have unique addresses.

ABB invented and manufactured many products and technologies, including the world’s first three-phase power transmission system, the world’s first self-cooling transformer, high-voltage direct current transmission technology and the first electric industrial robot, and pioneered their commercial application. ABB has a wide range of product lines, including a full range of power transformers and distribution transformers, high, medium and low voltage switchgear products, AC and DC transmission and distribution systems, power automation systems, various measuring equipment and sensors, real-time control and optimization systems, robotics hardware and software and simulation systems, energy-efficient motors and drive systems, power quality, conversion and synchronization systems, and other systems. Fusing and switching equipment to protect the safety of power systems. These products have been widely used in industry, commerce, power and public utilities.

ABB is one of the world’s top 500 companies (256th in 2008, 230th in 2009, 237th in 2010), with sales of $32 billion in 2009-2011. It is listed on the Zurich, Stockholm and New York Stock exchanges.

A safety loop is a loop of interlocking control that protects the load or control object and prevents operational errors or control failures. In the direct control of the load at the same time, the safety protection loop to the PLC input signal, in order to facilitate the PLC protection processing. Safety circuits generally consider the following aspects.

(1) Short-circuit protection should be installed in the PLC external output circuit fuse, short-circuit protection. It is best to install a fuse in the circuit of each load.

(2) Interlock and interlock measures in addition to ensuring the interlock relationship of the circuit in the program, the external wiring of the PLC should also take hardware interlock measures to ensure the safe and reliable operation of the system.

(3) Voltage loss protection and emergency shutdown measures PLC external load power supply line should have voltage loss protection measures, when the temporary power failure and then restore power supply, do not press the “start” button PLC external load can not start by itself. Another function of this wiring method is that when emergency shutdown is required under special circumstances, the load power supply can be cut off by pressing the “emergency stop” button, and the “emergency stop” signal is input to the PLC.

(4) Limit protection In some cases such as elevator class exceeding the limit may produce danger, set the limit protection, when the limit protection action directly cut off the load power supply, while the signal input PLC.

ABB GFD233A