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1、外文翻译译文S7-200的特性S7-200提供了几条特殊的性能帮助您更好地运用S7-200的功能，完成应用程序。S7-200允许您在程序中立即读写I/O在S7-200的指令集中提供了立即读写物理I/O点的指令。尽管通常情况下我们使用映像寄存器作为源地址和目的地址来访问I/O，但这些立即I/O指令却允许我们直接访问真正的输入、输出点。当使用立即指令访问一个输入点时，相应的过程映像输入寄存器不会发生改变。而当您使用立即指令访问一个输出点时，相应的过程映像输出寄存器会被同步刷新。提示除非您启用了模拟量输入滤波功能，否则S7-200将直接从模块上读取模拟量输入值。当您将一个数值写到模拟量输出时，输出值
2、会立即更新。通常认为在执行应用程序时，用过程映像寄存器会比使用直接访问输入、输出具有优越性。之所以这样有以下三个原因： 1.所有输入点的采样是在扫描周期的一开始同步进行的。在整个扫描周期的程序执行过程中输入值被冻结。而输出点按照映像寄存器中的值刷新是在程序执行完成之后。这样会使系统更加稳定。 2.访问映像寄存器的速度比直接访问I/O点要快，有利于程序快速运行。 3. I/O点是位实体，只能按位或者字节来访问，而您可以按位、字节、字或者双字的形式来访问映像寄存器。通过这种方式，映像寄存器将为您提供额外的灵活性。S7-200允许在程序扫描周期中使用中断如果您使用了中断，与中断事件相关的中断程序作为
3、程序的一部分被保存。中断程序并不作为正常扫描周期的一部分来执行，而是当中断事件发生时才执行(可能在扫描周期的任意点)。在中断优先级相同的情况下，S7-200遵循先来先服务的原则来执行中断程序。S7-200允许您为运行模式编辑和执行状态分配处理时间您可以设定一个扫描周期的百分比用来处理运行模式编辑或执行状态相关的通讯请求。(运行模式编辑和执行状态是STEP 7-Micro/WIN提供的备选功能，能使您更轻松地调试程序。) 在您增加用于通讯请求处理时间百分比的同时，扫描时间也会随之增加，从而会导致控制过程运行速度变慢。在默认设置下，用于处理运行模式编辑和执行状态通讯请求的时间百分比为10%。这个默
4、认设置为在对控制过程影响最小的前提下处理编译和状态操作，提供了一个合理的时间。您可以在5%到50%之间调节这个值。要想设置背景通讯的扫描周期时间片，按以下步骤：1. 点选视图 组件 系统块菜单命令并选中“背景时间”。2. 在“背景”标签下，通过下拉选框选择通讯背景时间。3. 点击“确定”保存您的选择。4. 将改变后的系统块下载到S7-200中。S7-200允许您设置停止模式下的数字量输出状态S7-200的输出表允许您选择STOP模式下的输出状态，是将已知值传送到数字量输出点，还是使输出保持STOP模式之前的状态。输出表是系统块的一部分，它被下载并储存在S7-200中。1. 选择视图 组件 系统
5、块菜单命令并选择输出表。点击“数字量”标签。2. 如果要冻结上一个状态的输出，选择“冻结输出”复选框。3. 如果要将输出表中的值复制到输出点上，则要填写输出表。在您希望从运行到停止模式转换后置1的相应位置上点击。输出表的缺省设置全部为0。4. 点击“确定”保存您的选择。5. 将改变后的系统块下载到S7-200中。S7-200允许您设置模拟量输出值模拟量输出表可以用来设置模拟量输出点，指明在从运行模式进入停止模式后，是将已知值传送至模拟量输出点，还是使输出保持停止模式之前的状态。模拟量输出表是下载并储存在S7-200中的系统块的一部分。1. 选择视图 组件 系统块菜单命令并选择“输出表”。点击“
6、模拟量”标签。2. 如果要冻结上一个状态的输出，选择“冻结输出”复选框。3. 在从运行模式进入停止模式时，通过冻结值表，您可以将模拟量输出点设为一个已知值(-32768到37262)。4. 点击“确定”保存您的选择。5. 将改变后的系统块下载到S7-200中。S7-200允许您定义掉电保护存储区如果您希望在掉电后仍然保持存储区中的数据，您可以定义最多六个掉电保护区的地址范围。可以将下列存储区中的地址范围定义为具有保持性：V、M、C和T。对于定时器，只有保持型定时器(TONR)可以设为掉电保护的。在缺省情况下，M存储器的前14个字节是非保持的。只能保留定时器和计数器的当前值：定时器和计数器位不具
7、有保持性。提示如果将地址范围MB0至MB13定义为保持，则在掉电时，这个区域里的值就会自动保存到永久存储器中。按照以下步骤设置掉电保护区：1. 点选视图 组件 系统块菜单命令并选中“保留范围”。2. 设置掉电保护区的范围并单击“确定”。3. 将改变后的系统块下载到S7-200中。S7-200允许对数字量输入进行过滤S7-200允许您为某些或者全部本机数字量输入点选择输入滤波器，并为滤波器定义延迟时间(从0.2ms到12.8ms可选)。这一延迟时间有助于滤除输入杂波，从而减小了输入状态发生意外改变的可能。输入滤波器是系统块的一部分，它被下载并存储在CPU中。滤波器延迟时间的缺省值为6.4 ms。
8、如图5所示，一组输入点共用一个延迟时间。按照以下步骤设置输入滤波器延迟时间：1. 点选视图 组件 系统块菜单命令并选中“输入滤波器”。点击“数字”标签。2. 为每一组输入指定延迟时间。3. 将改变后的系统块下载到S7-200中。提示数字量输入滤波器会对读取输入指令、输入中断和脉冲捕获产生影响。根据您的选择，应用程序有可能丢掉一个中断事件或者脉冲捕获。高速计数器不受此影响。S7-200允许您对模拟量输入加滤波器S7-200允许您对每一路模拟量输入选择软件滤波器。滤波值是多个模拟量输入采样值的平均值。滤波器参数(采样次数和死区)对于允许滤波的所有模拟量输入是相同的。滤波器具有快速响应的特点，可以反
9、映信号的快速变化。当输入与平均值的差超过设定的变化时，滤波器对最近的模拟量输入值产生一个阶跃函数。这个差称为死区，并用模拟量输入的数字信号设定。缺省组态将对所有的模拟量输入进行滤波，但CPU224XP上的AIW0和AIW2除外。1. 点选视图 组件 系统块菜单命令并选中“输入滤波器”。点击“模拟量”标签。2. 选择需要滤波的模拟量输入、采样个数和死区。3. 单击“确定”。4. 将改变后的系统块下载到S7-200中。提示不要对在模拟量字中传递数字信息或者报警指示的模块使用模拟量输入滤波。对于RTD、TC和ASI主站模块，不能使用模拟量输入滤波。提示CPU224XP上的AIW0和AIW2由模数转换
10、器来滤波，且通常无需另外的软件滤波。S7-200允许您捕捉窄脉冲S7-200为每个本机数字量输入提供脉冲捕获功能。脉冲捕获功能允许PLC捕捉到持续时间很短的高电平脉冲或者低电平脉冲。而在扫描周期的开始，这些脉冲不是总能被CPU读到。当一个输入设置了脉冲捕获功能时，输入端的状态变化被锁存并一直保持到下一个扫描循环刷新。这就确保了一个持续时间很短的脉冲能被捕捉到，并一直保持到S7-200读取输入点。可以分别启用每一个本机数字量输入点的脉冲捕获功能。按照以下步骤设置脉冲捕获：1. 点选视图 组件 系统块菜单命令并选中“脉冲捕获位”。2. 点击相应的复选框并点击“确定”。3. 将改变后的系统块下载到S
11、7-200中。S7-200提供高速I/O高速计数器S7-200具有集成的高速计数功能，它能够对外部高速事件计数而不影响S7-200的性能。不同CPU支持的计数速率，参见附录A。每个计数器有用于时钟、方向控制、复位和启动的专用输入，这种情况下可支持这些功能。在不同的模式下有不同的计数速率。高速脉冲输出S7-200支持高速脉冲输出功能，其输出点Q0.0和Q0.1可形成高速脉冲串输出(PTO)或脉宽调制(PWM)。PTO输出方波(占空比50%)，并可指定所输出的脉冲数量(从1到4,294,967,295)和周期(以微秒或毫秒为单位)。脉冲序列输出(PTO)功能可以编程为产生一列脉冲或产生由多个脉冲序
12、列组成的脉冲包络。在脉冲包络操作方式中，PTO功能被编程为控制一个步进电机运行一个简单的斜坡上升、运行和斜坡下降操作序列或更复杂的操作序列。PWM功能提供具有可变占空比的固定周期的输出脉冲，周期和脉宽既可以用微秒又可以用毫秒为单位。当脉宽等于周期时，占空比为100，输出恒定为1； 当脉宽等于0时，占空比为0，输出恒定为0。外文翻译原文Features of the S7-200The S7-200 provides several special features that allow you to customize how the S7-200 functions to better fi
13、t your application.The S7-200 Allows Your Program to Immediately Read or Write the I/OThe S7-200 instruction set provides instructions that immediately read from or write to the physical I/O. These immediate I/O instructions allow direct access to the actual input or output point, even though the im
14、age registers are normally used as either the source or the destination for I/O accesses.The corresponding process-image input register location is not modified when you use an immediate instruction to access an input point. The corresponding process-image output register location is updated simulta
15、neously when you use an immediate instruction to access an output point.TipThe S7-200 handles reads of analog inputs as immediate data, unless you enable analog input filtering. When you write a value to an analog output, the output is updated immediately.It is usually advantageous to use the proces
16、s-image register rather than to directly access inputs or outputs during the execution of your program. There are three reasons for using the image registers: - The sampling of all inputs at the start of the scan synchronizes and freezes the values of the inputs for the program execution phase of th
17、e scan cycle. The outputs are updated from the image register after the execution of the program is complete. This provides a stabilizing effect on the system. - Your program can access the image register much more quickly than it can access I/O points, allowing faster execution of the program. - I/
18、O points are bit entities and must be accessed as bits or bytes, but you can access the image register as bits, bytes, words, or double words. Thus, the image registers provide additional flexibility.The S7-200 Allows Your Program to Interrupt the Scan Cycle If you use interrupts, the routines assoc
19、iated with each interrupt event are stored as part of the program. The interrupt routines are not executed as part of the normal scan cycle, but are executed when the interrupt event occurs (which could be at any point in the scan cycle).Interrupts are serviced by the S7-200 on a first-come-first-se
20、rved basis within their respective priority assignments. The S7-200 Allows You to Allocate Processing Time for Run Mode Edit and Execution Status You can configure a percentage of the scan cycle to be dedicated for processing a run mode edit compilation or execution status. (Run mode edit and execut
21、ion status are options provided by STEP 7-Micro/WIN to make debugging your program easier.) As you increase the percentage of time that is dedicated to these two tasks, you increase the scan time, which makes your control process run more slowly. The default percentage of the scan dedicated to proce
22、ssing run mode edits and execution status is set to 10%. This setting was chosen to provide a reasonable compromise for processing the compilation and status operations while minimizing the impact to your control process. You can adjust this value by 5% increments up to a maximum of 50%. To set the
23、scan cycle time-slice for background communications: 1. Select the View Component System Block menu command and select Background Time. 2. In the Background tab, use the drop down box to select the communications background time. 3. Click OK to save your selection. 4. Download the modified system bl
24、ock to the S7-200.The S7-200 Allows You to Set the States of Digital Outputs for Stop Mode The output table of the S7-200 allows you to determine whether to set the state of the digital output points to known values upon a transition to the STOP mode, or to leave the outputs in the state they were i
25、n before the transition to the STOP mode. The output table is part of the system block that is downloaded and stored in the S7-200. 1. Select the View Component System Block menu command and select Output Table. Click on the Digital tab. 2. To freeze the outputs in their last state, select the Freez
26、e Outputs checkbox. 3. To copy the table values to the outputs, enter the output table values by clicking the checkbox for each output bit you want to set to On (1) after a run-to-stop transition. The default values of the table are all zeroes. 4. Click OK to save your selections. 5. Download the mo
27、dified system block to the S7-200.The S7-200 Allows You to Configure the Value of Analog Outputs The Analog Output Table allows you to set analog output points to known values after aRUN-to-STOP transition, or to preserve the output values that existed before the transition toSTOP mode. The Analog O
28、utput table is part of the system block that is downloaded and stored in the S7-200 CPU. 1. Select the View Component System Block menu command and select Output Table. Click on the Analog tab. 2. To freeze the outputs in their last state, select the Freeze Outputs check box. 3. The Freeze Values ta
29、ble allows you to set the analog outputs to a known value (-32768 to 37262), on a RUN-to-STOP transition. 4. Click OK to save your selections. 5. Download the modified system block to the S7-200.The S7-200 Allows You to Define Memory to Be Retained on Loss of Power You can define up to six retentive
30、 ranges to select the areas of memory you want to retain through power cycles. You can define ranges of addresses in the following memory areas to be retentive: V, M, C, and T. For timers, only the retentive timers (TONR) can be retained. The default setting for the first 14 bytes of M Memory is to
31、be non-retentive. Only the current values for timers and counters can be retained: the timer and counter bits are not retentive. Tip Changing the range MB0 to MB13 to be retentive enables a special feature that automatically saves these locations to the permanent memory on power down. To define the
32、retentive memory: 1. Select the View Component System Block menu command and select Retentive Ranges. 2. Select the ranges of memory to be retained following loss of power and click OK. 3. Download the modified system block to the S7-200.The S7-200 Allows You to Filter the Digital Inputs The S7-200
33、allows you to select an input filter that defines a delay time (selectable from 0.2 ms to 12.8 ms) for some or all of the local digital input points. This delay helps to filter noise on the input wiring that could cause inadvertent changes to the states of the inputs. The input filter is part of the
34、 system block that is downloaded and stored in the S7-200. The default filter time is 6.4 ms. As shown in Figure 4, each delay specification applies to groups of input points. To configure the delay times for the input filter: 1. Select the View Component System Block menu command and select Input F
35、ilters. Click on the Digital tab. 2. Enter the amount of delay for each group of inputs and click OK. 3 Download the modified system 3. Download the modified system block to the S7-200. Tip The digital input filter affects the input value as seen by instruction reads, input interrupts, and pulse cat
36、ches. Depending on your filter selection, your program could miss an interrupt event or pulse catch. The high speed counters count the events on the unfiltered inputs.The S7-200 Allows You to Filter the Analog Inputs The S7-200 allows you to select software filtering on individual analog inputs. The
37、 filtered value is the average value of a preselected number of samples of the analog input. The filter specification (number of samples and deadband) is the same for all analog inputs for which filtering is enabled. The filter has a fast response feature to allow large changes to be quickly reflect
38、ed in the filter value. The filter makes a step function change to the latest analog input value when the input exceeds a specified change from the current value. This change, called the deadband, isspecified in counts of the digital value of the analog input. The default configuration is to enable
39、filtering for all analog inputs except AIW0 and AIW2 on CPU 224XP. 1. Select the View Component System Block menu command and select Input Filters. Click on the Analog tab. 2. Select the analog inputs that you want to filter, the number of samples, and the deadband. 3. Click OK. 4. Download the modi
40、fied system block to the S7-200.Tip Do not use the analog filter with modules that pass digital information or alarm indications in the analog words. Always disable analog filtering for RTD, Thermocouple, and AS-Interface Master modules. Tip AIW0 and AIW2 on the CPU 224XP are filtered by the analog
41、to digital converter, and usually will not need the additional software filter.The S7-200 Allows You to Catch Pulses of Short DurationThe S7-200 provides a pulse catch feature which can be used for some or all of the local digital input points. The pulse catch feature allows you to capture high-goin
42、g pulses or low-going pulses that are of such a short duration that they would not always be seen when the S7-200 reads the digital inputs at the beginning of the scan cycle. When pulse catch is enabled for an input, a change in state of the input is latched and held until the next input cycle updat
43、e. This ensures that a pulse which lasts for a short period of time is caught and held until the S7-200 reads the inputs.You can individually enable the pulse catch operation for each of the local digital inputs.To access the pulse catch configuration screen:1. Select the View Component System Block
44、 menu command and select Pulse Catch Bits.2. Click the corresponding check box and click OK.3. Download the modified system block to the S7-200.The S7-200 Provides High-speed I/O High-Speed Counters The S7-200 provides integrated high-speed counter functions that count high speed external events wit
45、hout degrading the performance of the S7-200. See Appendix A for the rates supported by your CPU model. Each counter has dedicated inputs for clocks, direction control, reset, and start, where these functions are supported. You can select different quadrature modes for varying the counting rate. Hig
46、h-Speed Pulse Output The S7-200 supports high-speed pulse outputs, with outputs Q0.0 and Q0.1 generating either a high-speed pulse train output (PTO) or pulse width modulation (PWM). The PTO function provides a square wave (50% duty cycle) output for a specified number of pulses (from 1 to 4,294,967
47、,295 pulses) and a specified cycle time (in either microsecond or millisecond increments. You can program the PTO function to produce either one train of pulses or a pulse profile consisting of multiple trains of pulses. For example, you can use a pulse profile to control a stepper motor through a simple ramp up, run, and ramp down sequence or more complicated sequences. The PWM function provides a fixed cycle time with a variab