How to Calculate the Capacitor of the Reset Input of a C51 Microcontroller
How to Calculate the Capacitor of the Reset Input of a C51 Microcontroller
This application note explains how the reset of the 80C51 microcontroller works when the RST pin is a pure input pin and when the RST input is bi-directional. It gives rules to determine the extra components required to operate the reset function properly. The reset process can be active on low or high level depending on the product. In this application note only the high level case is discussed.
Introduction
The reset is used to start-up or to restart the 80C51 microcontroller activities. It forces the 80C51 in a known state by reinitializing all the internal registers needed to properly start the program execution. The reset must be kept active until all three of the follow-ing conditions are respected:
?The power supply must be in the specified range.
?The oscillator must reach a minimum oscillation level to ensure a good noise to signal ratio and a correct internal duty cycle generation.
?The reset pulse width duration must be at least two machine cycles.
If one of the conditions is not respected the microcontroller will not startup properly. Theory of Reset Operation
To ensure a good startup, the reset pulse width has to be wide enough to cover the period of time where the electrical conditions are not met. Two parameters should be considered for a proper reset sequence to determine the reset pulse width (see Figure1):
?t osc: time needed by the oscillator to reach the Vih1 or Vil1 level.
?t vddrise: rise time of the power-supply taken between 10 to 90% of V DD.
When these two parameter conditions are met, the reset has to be maintained at least two machine cycles in order to synchronize the internal activity of the core. In normal
mode, a machine cycle is 12-clock periods and in X2 mode is 6-clock periods.
2
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Figure 1. t osc and t vddrise are the Two Parameters to Evaluate, Depending on the Application
Vih1 is the reference parameter taken to calculate and determine the time constant of the reset. Indeed, normally the input is considered to be low when its level reaches Vil1.But in reality the trigger is somewhere between Vih1 and Vil1. So, the worst case condi-tion is considered at the Vih1 level.
When the reset is released, the program execution starts and the ALE signal toggles as it is illustrated in Figure 2. and showing a proper startup condition:?V DD is within the voltage operating range,
?The level of Xtal1 is greater than the Vih1 level specification,
?The reset reached its active level (Vih1) and is maintained at least two machine
cycles.Figure 2. Reset Conditions to Properly Startup a Microcontroller
t vddrise
t osc
Vih1
treset V DD
XTAL1
V DD
V DD Vrst
XTAL2
Reset is released
ALE
3
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Why Does the Reset Does Not Properly Start the Microcontroller?
The Oscillator is not Stabilized
Figure 3 shows the case where the RST signal is applied while the oscillator is not stabi-lized and there is no clock to reset the internal registers of the CPU. Due to this bad reset, the first address fetched can be anywhere in the program space except address 0000h.
Figure 3. If electrical Conditions are not Met, the Reset Signal is Applied but without the Clock
Reset is Released before V DD is Stable Figure 4 shows the case where the reset is released before the V DD is stable. The micro-controller will never see the reset and can start anywhere in the program space and with
a bad register initialization.
Figure 4. The Reset is Released before the Clock and the V DD are Stable
V DD
Vrst
XTAL2
ALE
The reset is applied while the clock is not stabilized
V DD
Vrst
XTAL2
ALE
4
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Reset Input Circuitry Description
At least two kinds of reset input structure exist in C51 products. The first one is a pure input which allows an external device to reset the microcontroller. The second one is bi-directional. The microcontroller can be reset by an external device. The microcontroller can reset an external device when, for example the internal watchdog expires. Table 1lists some C51 Atmel products which have uni-directional or bi-directional reset.uni-directional Reset Input
Description
The uni-directional reset input circuitry is shown in Figure 5. A pull-down resistor, Rrst ,is connected between the RST input and the ground. An external capacitor, Crst , is con-nected between the RST input and the V DD . The value of Crst determines the reset time duration. The calculation of Crst is explained in the next chapter.
Figure 5. Reset Structure for an uni-directional Circuitry
Theory of Operation
When a reset is applied on the RST input, Crst is discharged and then charged through Rrst . The reset is active until the level applied on the RST pin is below Vih1. Crst deter-mines the reset pulse width duration.
Table 1. Examples of Products Using Uni-directional and Bi-directional Reset
Product Main Features Uni/Bidir
T83C51RB216 KB of ROM, Watchdog B T89C51RD264 KB of Flash, Watchdog B AT89C51CC0110-bit ADC, CAN controller B AT89C51SND1
MP3 decoder, TWI, MMC, USB
U
5
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Bi-directional Reset Input
Description
The bi-directional reset circuitry is shown in Figure 6. In addition to the uni-directional structure, the RST pin is able to drive an external reset for example when a watchdog expires. To do this, a pull-up resistor (Rrstwt ) controlled by the rstcon signal drives a high level on the RST pin. An extra resistor (Rrstext) must be added between the RST input and Crst (Figure 6.).
Figure 6. Reset Structure in a Bi-directional Mode
Theory of Operation External Reset
During a power-up or when an external reset is applied to the RST input, the Crst capacitor is charged through the two resistors Rrstext and Rrst . The reset is active until the level applied on the RST pin is below Vih1. The Rsrtext resistor is required when an internal reset is applied by the microcontroller and will be explained in the next session.Internal Reset
In some cases, such as a watchdog reset, the microcontroller generates an internal reset by driving the rstcon signal and consequently by applying a high level on the RST pin. The pulse duration depends on the product and is typically equal to 96 clock periods (see the product datasheet).
The Rrstext allows a reset pulse to occur on the RST pin. The reset time constant (sev-eral ms) is large in comparison to the reset pulse duration (96 clock periods). In that condition, Crst maintains its charge (V DD ) for all the duration of the reset pulse even if Rrstwt is active (see Figure 7). V DD is applied across the Rrst and Rrstwt resistors and expression of Vrst is given below:
For a given Rrstwt resistance, Rrstext determines the active level of the reset pin. To take into account on the external and internal reset constraints, Rrstext must be chosen in the 1 k ? and 10 k ? range.
Vrst VDD Rrstext
Rrstext Rstwt +-------------------------------------------×=
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Figure 7.
Without Rrstext no external reset signal will be generated.
Use Excel File to Determine Crst
To determine Crst, the reset pulse width needs to be calculated using the following equation:
treset = t vddrise + t osc
?t vddrise (typically 1 ms to 100 ms), is the rise time of the V DD (10% and 90% of the V DD ). It depends on the power supply and the decoupling capacitors used.
?
t osc (typically 1 ms to 50 ms), time taken by the oscillator at startup. It depends on the crystal characteristics and the capacitors connected to the crystal.
Because the power supply has a finite transition time (several hundreds of microsec-onds to several milliseconds), Crst is not so easy to compute by hand. Excel tool is used to calculate Crst versus t vddrise and t osc parameters. A spreadsheet can be down-loaded from the Atmel Web site to compute Crst .
Four parameters have to be entered and Crst is directly computed by the spreadsheet while 1k ? is chosen for Rrst . Here is how to do it:
?V DD , the power supply voltage, is entered in the cell F3
?t vddrise , the rise time of the power-supply, is entered in the cell F4?t osc , the oscillator startup time, is entered in cell F8
?Rrstmin , the minimum pull-down resistor, is entered in the cell F13
After these steps, the cell E31 has to be clicked to compute the Crst and the minimum reset pulse width.
V DD
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Table 2. Excel Spreadsheet Use to Calculate Crst
Table 3 gives the Crst value computed from the Excel file for different values of t vddrise and t osc parameters.
Table 3. Minimum Reset Capacitor Value for a 50k ? Pull-down Resistor (Rrstmin )
Table 4. Minimum Reset Capacitor Value for a 100K ? Pull-down Resistor
Power Supply Characteristics
Power Supply Voltage
V DD =
5V Power Supply Rise Time (10% to 90%)
tvddrs =
1
ms
Oscillator
Oscillator Startup Time time, measured at VIH1
tosct =
10
ms
Electrical Characteristics of the Reset Input
Minimum pull-down resistance
Rrstmin =
100
k ?
Minimum Pulse Width
Calculation of the reset pulse width
trstmin =
22, 726
ms
Evaluation of Reset Capacitor: C
Minimum reset pulse width Trst = 65, 545ms Value of reset capacitor C
C =
0.649
μF
t osc
t vddrise
1 ms 10 ms 100 ms 5 ms 820 nF 1.
2 μF 12 μF 20 ms
2.7 μF
3.9 μF
12 μF
t osc
t vddrise
1 ms 10 ms 100 ms 5 ms 390 nF 0.56 μF 5.6 μF 20 ms
1.2 μF
2 μF
5.6 μF
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(易错题精选)初中英语词汇辨析的单元汇编含答案解析
一、选择题 1．I’d like to________the mall because it’s crowded and noisy. A．visit B．hang out C．walk D．go off 2．That path ________ directly to my house.You won't miss it. A．leads B．forms C．repairs D．controls 3．I don’t want to go. __________, I am too tired. A．However B．And C．Besides D．But 4．Some animals carry seeds from one place to another, ________ plants can spread to new places. A．so B．or C．but D．for 5．When I as well as my cousins __________ as a volunteer in Beijing, I saw the Water Cube twice. A．were treated B．treated C．was served D．served 6．He is wearing his sunglasses to himself from the strong sunlight. A．prevent B．stop C．keep D．protect 7．When you are________, you should listen to music to cheer you up. A．shy B．afraid C．strict D．down 8．Mr. Smith gave us some________on how to improve our speaking skills. A．advice B．news C．knowledge D．information 9．World Book Day takes place ________ April 23rd every year. A．at B．in C．on 10．More and more people have realized that clear waters and green mountains are as ________ as mountain of gold and silver. A．central B．harmful C．valuable D．careful 11．We loved the food so much, ________the fish dishes. A．special B．especial C．specially D．especially 12．—Oh, my God! I have ________ five pounds after the Spring Festival. —All of the girls want to lose weight, but easier said than done. A．given up B．put on C．got on D．grown up 13．—What do you think of the performance today? —Great! ________ but a musical genius could perform so successfully. A．All B．None C．Anybody D．Everybody 14．He ________ his homework________the morning of Sunday. A．doesn’t do; on B．doesn’t do; in C．doesn’t; on 15．Maria ________ speaks Chinese because she doesn’t know much Chinese. A．seldom B．always C．often D．usually 16．In 2018, trade between China and Hungary rose by 7.5 percent, and recently on Friday companies from China and Hungary________ several cooperation (合作) agreements under the
人教版初一英语现在进行时
现在进行时 撰稿：王红艳审稿：白雪雁 【概念引入】 I. 什么是现在进行时？ 1）现在进行时表示说话时正在进行或发生的动作。 例如：I am reading a book. 我正在看书。 2）表示现阶段正在进行而说话时不一定在进行的动作。 例如：I am learning English hard these days. 这些日子我正在努力学习英语。 II. 现在进行时的标志词。 现在进行时常和now、at the moment、look、listen等连用。 【用法讲解】 I.现在进行时的结构。 现在进行时的结构是：助动词be（am，is，are）＋现在分词v-ing 现在分词的构成： 1）动词的后面直接加－ing。例如：work－working，study－studying 2）以不发音的字母e结尾的动词，先去掉字母e，再加－ing。例如：live－living 3）以重读闭音节结尾并且只有一个辅音字母的动词，先双写这个辅音字母，再加－ing。 例如：stop－stopping，swim－swimming，run－running II. 现在进行时的用法。 1）现在进行时表示说话的时候正在进行的动作，经常和now，right now，at the moment 等时间状语或者动词look，listen等连用。 例如：My father is watching TV now.我爸爸现在在看电视。 Look! My brother is playing basketball there. 看！我弟弟正在那里打篮球。 2）现在进行时可以表示目前一段时间内一直进行的动作，经常和these days，this week，at present等时间状语连用。 例如：My parents are working on a farm these days. 这些天我的父母在农场干活。 3）现在进行时还可以表示现在不断发展变化的事情，表示不断发展变化的动词有get，grow，turn，become等。 例如：The leaves are turning yellow. 树叶在变黄。 4）现在进行时还可以表示将要发生的动作，只限于动词arrive，begin，go，come，leave，fly等动词。 例如：I am coming soon. 我马上来。 Ⅲ. 现在进行时的句式变化。 肯定句式：主语+be( am, is, are)+现在分词+其它. 否定句式：主语+be(am, is, are) +not +现在分词+其它. 一般疑问句：Be(am, is, are) +主语+现在分词+其它？ 特殊疑问句：疑问词+be(am, is, are)+主语+现在分词+其它？ 对现在进行时的特殊疑问句的回答，它不可以用Yes或No直接作答，要根据实际情况回答。 Ⅳ. 现在进行时的特殊用法。 表示位置移动的动词，如：leave/ come/go/begin等用于现在进行时，表示按计划或安排近期将要进行的动作，常与表示将来的时间状语连用。 —Can you help me? 你能帮我吗？
第三次英语作业答案
精读二作业(3) 翻译题： I.Translate the following phrases into English: 1．面临诱惑be faced with the temptation 2. 对学生们过分严厉be hard on the students 3. 认为某事当然Take something for granted 4. 编智力测试题make up the intelligence tests 5. 表扬的温暖阳光The sunlight of praise 6. 靠吃野菜生活live on wild plants 7. 对老师的话不予理睬shrug off the teacher’s words 8. 转达一句赞美的话pass on a compliment II.Translate the following sentences into English: 1.据说，他们为新建一所山村小学开展筹款运动。 It is said that they launched a campaign to raise money for a mountain village primary school. 2. 如果你总是偷东西，肯定不会有好下场的。 If you keep stealing you will surely come to a bad end. 3不要想当然地认为大学毕业生就什么都能做。 Don’t take it for granted that college graduates can do everything in all aspects
boring 令人厌烦的
boring 令人厌烦的，乏味的，无聊的 tedious 乏味的，单调的，冗长的 flat 单调的，沉闷的 dull 乏味的，单调的 troublesome 令人烦恼的，讨厌的，麻烦的 tired 疲劳的，累的 bored 无聊的，无趣的，烦人的 exhausted 极其疲倦的 weary 疲劳的 bright 聪敏的，机灵的 apt 聪明的，反应敏捷的 intelligent 聪明的，有才智的 shrewd 机灵的，敏锐的，精明的（表示生意上的精明） ingenious （人，头脑）灵巧的 alert 警觉的，留神的 cute 聪明伶俐的，精明的 acute/cute acute 指的是视力，感觉的敏锐 dull 愚钝的，笨的 awkward 笨拙的，不灵巧的 absurd 荒谬的 ridiculous 可笑的，荒谬的 idiotic 白痴般的 blunt 率直的，直言不讳的 clumsy 笨拙的，粗陋的 happy 快乐的，幸福的 cheerful 欢乐的，高兴的 content 满意的，满足的 merry 欢乐的，愉快的，快乐的 pleasure 高兴，愉快，满足 enjoyment 享乐，快乐，乐趣 cheer 喝彩 applause 鼓掌，掌声 optimism 乐观，乐观主义 delight 快乐，高兴 kick 极大的乐趣 paradise 天堂，乐园 instant 立即的，即刻的 instantaneous 瞬间的，即刻的 immediate 立即的，即刻的 simultaneous 同时发生的，同时存在的，同步的punctual 严守时刻的，准时的，正点的 pick 挑选，选择 select 选择，挑选 single 选出，挑出 elect 选举，推举 vote 投票，选举 appoint 任命，委派 nominate 提名，任命 propose 提名，推荐 recommend 推荐，举荐 designate 指派，委任 delegate 委派（或选举）…为代表 install(l) 使就职，任命 ballot 使投票表决 dub 把…称为 choice 选择（权） option 选择 selection 选择，挑选 alternative 取舍，供选择的东西 favorite 特别喜爱的人（或物） inclination 爱好 preference 喜爱，偏爱，优先 observe 注意到，察觉到 perceive 认识到，意识到，理解 detect 察觉，发现 appreciate （充分）意识到，领会，体会 alert 使认识到，使意识到 awake 意识到，醒，觉醒 scent 察觉 ancient 古代的，古老的 primitive 原始的 preliminary 预备的，初步的 preliminary trial初审 primary 最初的，初级的 initial 开始的，最初的 original 起初的 former 在前的，以前的 previous 先，前 prior 在前的，优先的 beforehand 预先，事先 medieval 中世纪的，中古（时代）的preceding 在先的，在前的，前面的 senior 资格较老的，地位较高的 following 接着的，下述的 attendant 伴随的 subsequent 随后的，后来的 succeeding 以后的，随后的 consequent 作为结果（或后果）的，随之发生的 resultant 作为结果的，因而发生的therefore 因此，所以 consequently 所以，因此 then 那么，因而 thus 因此，从而 hence 因此，所以 accordingly 因此，所以，于是 thereby 因此，从而
现在进行时特殊用法展现
现在进行时特殊用法展现 现在进行时表示说话时正在进行的动作，这是我们平时接触最多的。然而除此以外，现在进行时还有以下几种用法。 1．表示“在做某事的过程中”，此时动作不一定正在发生。例如： Next I'll give you a few minutes to read the article．When you are reading，make a mark where there is a new word．现在我给你们几分钟时间读一下这篇文章。在读的过程中，在有生词的地方作以标记。 2．表示按计划、方案或安排而进行的将来的动作。在这种情况下谓语动词多为非延续性动词，如come，go， leave，move，die，start，stop，arrive等，及少数延续性动词，如spend，stay等。例如： She is leaving for Guangzhou next week．她下星期就要去广州了。 We are spending the whole summer holiday inBeijing soon．不久我们要在北京度过整个暑假。 Where are you staying in Guangzhou？在广州你打算住什么地方？ 3．与副词forever，always，constantly等连用，表示赞成、厌烦、生气等情绪。例如： She is always talking loudly in our class．她总是在我们班上吵吵嚷嚷的。（表示厌烦） She's constantly changing her mind．她老是改变主意。（表示不以为然） He is forever complaining about his job．他总是对他的工作提出抱怨。（表示厌烦） 4．teach，work，live，study等表示状态的动词使用现在进行时可表状况，与一般现在时区别不大。例如： I'm studying in No．1Middle School．我在一中学习。（相当于：I study in No．1Middle School．） My brother is working in a big factory．我哥哥在一家大工厂工作。（相当于：My brother works in a big factory．） 5．表示目前经常发生的动作，然而此时动作不一定正在进行之中。例如：
大学英语II第三次作业(西南交大)
一、单项选择题(只有一个选项正确，共40道小题) 1. –What time is it? –____________________. (A) My watch keeps good time (B) My watch is five minutes fast (C) My watch says three o’clock (D) I say three o’clock 正确答案：C 解答参考：[第三单元] 本题问句是“现在几点钟”，C项“我的表是三点钟”。A项“我的表走时准确”，B项“我的表快五分钟”，D项“我说是三点钟”都不符合习惯表达法。 2. –Could you tell me the time, please? –____________________. (A) Yes, I can (B) No, I can’t (C) It’s four thirty (D) It’s Friday 正确答案：C 解答参考：[第三单元]C 本题仍是问时间，回答应该直接告诉对方时间，故C项正确。 3. –What day is tomorrow? –Today is Tuesday. So it’s________. (A) Monday (B) Wednesday (C) Thursday (D) Saturday 正确答案：B 解答参考：[第三单元]B 本题问“明天是星期几”，回答“今天是星期二，所以明天是星期三”。 4. –When is your birthday? –____________________. (A) It’s April 18th (B) It’s Sunday (C) It’s August
boring 和bored的区别
不能片面说人做主语用ed，物做主语ing ing形式是修饰引起这种感觉的人或物；ed形式是描写人或物的感受。（当然物一般是动物） 翻译的话 ing形式的词译为“令人……的”；ed形式译为“……的” boring是令人感到厌烦的；bored是厌烦的。 a boring person 能够指一个了无情趣的人，让人觉得无趣的人 a bored person 则是说这个人自己感到很无趣 1.bore 1）vt.使厌烦；挖 e.g. I'm bored with this job. 这件工作厌烦了。 The oldier bore the sharp pain in the wound with great courage. 这士兵以巨大的勇气忍受着伤口的剧烈疼痛。 2）n.令人讨厌的人（或事） e.g. It's a bore having to go out again. 外出真是讨厌。 boredom n.厌倦，无趣 e.g. in infinite boredom 极其无趣 boring n. 钻(孔) adj. 令人厌烦的(事或物） e.g. The play was boring. 这部短剧很一点意思都没有。 bored adj. 无聊的, 无趣的, 烦人的 e.g. Jack is so bored. 杰克是个没有趣的人。 2.surprising 是针对事或物感到惊奇。 surprised 则是针对人。 3.pleasant adj. 愉快的, 快乐的, 舒适的, 合意的可爱的, 举止文雅的, 活泼的滑稽的, 有趣的 (天气)晴朗的, 美好的容易相处的, 友爱的 e.g. a pleasant voice 悦耳的声音 a pleasant companion 可爱的伴侣 a pleasant time 愉快地度过时光 pleasing adj. 舒适的, 使人愉快的; 满意的; 惹人喜欢的, 可爱的 e.g. a pleasing look 使人愉快的神情 a very well mannered and pleasing young man 彬彬有礼而令人喜爱的年轻人
现在进行时_动词加ing的变化规律
现在进行时动词加ing的变化规律 1)一般情况下，直接加 -ing: 如：go—going answer—answering study—studying be—being see—seeing [注一] 和名词复数、一般现在时动词第三人称单数加-s(-es)不同， 动词末尾如为“辅音字母 + y”时，y不变，其后直接加ing。 如: study—studying fly—flying carry—carrying [注二] 动词结尾为辅音字母r时，加-ing，r在此必须发音。 如: water—watering answer—answering wear—wearing 2)以不发音的e结尾的动词，去掉e，再加ing 如：come—coming write—writing take—taking become—becoming 3)动词是闭音节的单音节词，或是以重读闭音节结尾的多音节词， 而末尾只有一个辅音字母时，这个辅音字母须双写，然后再加ing。 如：sit—sitting run—running stop—stopping begin—beginning admit—admitting forget—forgetting [注一] send，think，accept等动词虽是闭音节或以重读闭音节结尾， 但末尾有一个以上的辅音字母，因此，这个辅音字母不双写，应直接加ing。 如：sending thinking accepting 4)少数几个以-ie结尾的动词，须将ie变作y，再加ing。 如：die—dying tie—tying lie—lying躺，说谎 5)少数以-c结尾的动词变为现在分词时和过去式，须先将-c变为ck,然后再加-ing 或-ed 。 如：picnic—picnicking (picnicked) traffic—trafficking (trafficked)
计算机专业英语第3次作业
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现在进行时用法
现在进行时 一、定义及用法： 1定义：（1）表示说话时正在进行的动作及行为。（2）表示现阶段正在进行的动作。 2基本用法： (1)现在进行时主要表示说话人的说话时刻正在进行的动作、不断重复的动作或目前这个阶段（不一定是说话时刻）正在进行的动作，如： We’re having a meeting. 我们在开会。（说话时正在进行的动作） Be quiet！The baby is sleeping.安静，孩子在睡觉。 He is teaching in a middle school. 他在一所中学教书。（目前阶段在进行的动作） (2)现在进行时表将来: 现在进行时表将来，主要表示按计划或安排要发生的动作： I’m leaving tomorrow. 我明天走。 They’re getting married next month. 他们下个月结婚。 注意：现在进行时与一般现在时均可表示将来，区别是：用现在进行时表示将来，其计划性较强，并往往暗示一种意图；而一般现在时表示将来，则其客观性较强，即通常被视为客观事实，多指按时刻表或规定要发生的情况： I’m not going out this evening. 今晚我不准备出去。 What time does the train leave？火车什么时候开？ (3)现在进行时表示感情色彩: 现在进行时有时可表示满意、称赞、惊讶、厌恶等感情色彩，通常与always，forever，constantly，continually等副词连用。比较： She’s always helping people. 她老是帮助别人。（表赞扬） She always helps others. 他总是帮助别人。（陈述一个事实） The boy is constantly lying. 这孩子老是撒谎。（表示厌恶） The boy often lies. 这孩子常撒谎。（指出缺点） 二、结构: 现在进行时常有三种句型： （1）肯定式：主语＋be＋v-ing＋其它。 如：He is mending his bike．他正在修自行车。 （2）否定式：主语＋be＋not＋v-ing＋其它。 如：He is not（isn't）mending his bike．他没在修自行车。 （3）疑问式：主要分一般疑问句和特殊疑问句两种句式。 一般疑问句：Be＋主语＋v-ing＋其它？ 如：—Is he mending his bike？他正在修自行车吗？—Yes，he is．（No，he isn't．）特殊疑问句：疑问词＋be＋主语＋v-ing＋其它？ 如：—What is he doing？他正在干什么？ 三、何时用现在进行时？ （1）以Look！或Listen！开头的句子提示我们说话时动作正在进行，应用现在进行时。 如：Look！The children are playing games over there． Listen！Who's singing in the classroom？ （2）当句子中有now（现在）时，常表示说话时动作正在进行，这时也常用现在进行时。 如：We are reading English now． （3）描述图片中的人物的动作时常用现在进行时，以示生动。 如：Look at the picture．The girl is swimming． （4）表示当前一段时间内的活动或现阶段正在进行的动作时常用现在进行时。这时常与时间状语these days，this week等连用。
2018专业英语第一次作业(一二课内容)
湖南文理学院学院2017-2018学年度第一次作业 考核课程： 《计算机专业英语》 学生所在院系： 国际学院 年 级： 2017 姓名： 刘飞 班级： 网工17102班 学号： 201719040213 一、Give out the full names for the following abbreviations(写出下列缩写词的全称)（２0%） EEPROM_Electrically Erasable Programmable Read-Only Memory_ CPU ___Central Processing Unit____________________________ ALU ___A rithmetic/Logic Unit _______________________________ IT ___Information Technology___________________________ WWW___World Wide Web_________________________________ RAM ____Random Access Memory_________________________ PNP _____Plug-And-Play__________________________________ OS _____Operating System_______________________________ HTML____Hyper Text Markup Language______________________ TCP ____Transfer Control Protocol_________________________ SSI _____Small-Scale Integrated circuit_____________________ DRAM____Dynamic Random Access Memory________________ CA(M)D___Computer Aided Design__________________________ CAI_______Computer Aided Instruction______________________ 256000000__two hundreds and fifty six million________________ 25600000___twenty five million and six thousands_____________ SRAM_____Static Random Access Memory___________________ CAT_______Computer Aided Text____________________________ CA Ｍ______Computer Aided Made(Manufacture)_______________ Ｉ／Ｏ_____Input/Output__________________________________ 二、Match the following words and expressions in the left column with those similar in meaning in the right column( 将)（10%） 1. memory unit a. 半导体存储器 2. high density b. 主存
(易错题精选)初中英语词汇辨析的难题汇编及解析
一、选择题 1．Is this a photo of your son? He looks________ in the blue T-shirt. A．lovely B．quietly C．beautiful D．happily 2．—Jerry looks so tired. He works too hard. —He has to ________ a family of four on his own. A．offer B．support C．provide D．remain 3．— Mr. Wilson, can I ask you some questions about your speech? — Certainly, feel __________ to ask me. A．good B．patient C．free D．happy 4．Some animals carry seeds from one place to another, ________ plants can spread to new places. A．so B．or C．but D．for 5．— Can you tell us about our new teacher? —Oh, I’m sorry. I know________ about him because I haven’t seen him before. A．something B．anything C．nothing D．everything 6．—Help yourselves! The drinks are ________ me. —Thank you. You’re always so generous. A．above B．in C．on D．over 7．Gina didn’t study medicine. ________, she decided to become an actor. A．Instead B．Again C．Anyway D．Also 8．—Have you got Kathy’s________ for her concert? —Yes, I’d like to go and enjoy it. A．interview B．information C．invitation D．introduction 9．More and more people have realized that clear waters and green mountains are as ________ as mountain of gold and silver. A．central B．harmful C．valuable D．careful 10．Kangkang usually does her homework ________ it is very late at night. A．until B．when C．before D．after 11．He ________all the “No Smoking” signs and lit up a cigarette. A．requested B．attacked C．protected D．ignored 12．一Where is Mr. Brown? 一I think he's _____________ the music hall. A．on B．in C．over D．from 13．— Is your home close to the school, Tom? — No, it's a long way, but I am________ late for school because I get up early daily. A．always B．usually C．never D．sometimes 14．—Mum, I don’t want the trousers. They’re too long.
英语现在进行时用法
英语现在进行时用法 初中英语――现在进行时 1】现在进行时的构成 现在进行时由"be+v-ing"构成。be应为助动词，初学者最容易漏掉，它应与主语的人称和数保持一致。 2】现在进行时的应用 在实际运用时，现在进行时常用以下几种情况： (1)当句子中有now时，常表示动作正在进行，这时要用现在进行时。如： They are playing basketball now.现在他们正在打篮球。 (2)以look, listen开头的句子，提示我们动作正进行，这时要用现在进行时。如： Listen！She is singing an English song.听，她正在唱英语歌。 (3)表示当前一段时间或现阶段正在进行的动作，且此时有this week, these days等时间状语，这时常用现在进行时。如： We are making model planes these days.这些天我们在做飞机模型。 (4)描述图片中的人物的动作，也为了表达更生动。此时也常用现在进行时。如： Look at the picture. The children are flying kites in the park.看这幅图，那些孩子正在公园放风筝。 3】现在进行时的变化 肯定句式：主语+be( am, is, are)+现在分词+其它. 否定句式：主语+be(am, is, are) +not +现在分词+其它. 一般疑问句：Be(am, is, are) +主语+现在分词+其它？ 特殊疑问句：疑问词+be(am, is, are)+主语+现在分词+其它？ 对现在进行时的特殊疑问句的回答，它不可以用Yes或No直接作答，要根据实际情况回答。 注意事项 1.在英语中，并不是所有的动词都要使用正在进行时。例如一些表示状态和感觉的动词，一般不用进行时态，而是用现在一般时表示。例如： I hear someone singing. 我正听见有人唱歌。
大学英语三第三次在线作业
视窗 × loading... 大学英语三第三次在线作业 单选题 (共40道题) 展开 收起 1.（ 2.5分）– Can I help you? --__________. ?A、I want that blue dress. ?B、OK. ?C、That’s OK. ?D 、I can help you. 我的答案：A此题得分：2.5分 2.（2.5分）– What else do you want? -- ___________. ?A、Nothing else. ?B、I’m fine. ?C、What do you want? ?D、It doesn’t matter. 我的答案：A此题得分：2.5分 3.（2.5分）– What kind of room do you want? -- _____.
?A、Room 1. ?B、I have no idea. ?C、I want a single room. ?D、I’m sorry. 我的答案：C此题得分：2.5分 4.（2.5分）– Have you made a reservation? -- ____________. ?A、Yes, I have. ?B、I did. ?C、Yes, I will. ?D、Thank you. 我的答案：A此题得分：2.5分 5.（2.5分）–Excuse me, where can I check out? -- ____________. ?A、At the reception desk. ?B、You’re welcome. ?C、Nice to see you. ?D、When you are ready. 我的答案：A此题得分：2.5分 6.（2.5分）– I really enjoyed the concert. -- _______. ?A、What will you do tomorrow? ?B、I’m glad to hear that.
【英语】英语形容词常见题型及答题技巧及练习题(含答案)及解析
【英语】英语形容词常见题型及答题技巧及练习题(含答案)及解析 一、初中英语形容词 1．My deskmate is really _____．She likes to attend different activities after school． A. active B. quiet C. lazy D. honest 【答案】 A 【解析】【分析】我的同桌同学非常活跃，放学后喜欢参加很多不同的活动． 句中提到"She likes to attend different activities after school"放学后喜欢参加很多不同的活动，由此推测此人非常活跃，A积极的，活跃的；B安静的；C懒惰的，D诚实的，根据句意可知选择A． 2．Wang Wei speaks English as ________ as Yang Lan. They both study English hard. A. good B. well C. better D. best 【答案】 B 【解析】【分析】句意：王伟的英语讲的和杨澜的一样好。他们学习英语都努力。可知as…as中间用形容词或副词原级；此处是副词修饰动词speak。good好的，形容词原形；well好地，副词原形，better比较级；best最高级，故选B。 【点评】此题考查形容词原级。注意as...as中间跟形容词或副词原级。 3．—If there are ________ people driving, there will be ________ air pollution. —Yes, and the air will be fresher. A. less; less B. less; fewer C. fewer; fewer D. fewer; less 【答案】 D 【解析】【分析】句意：——如果开车的人越少，空气污染越少。——是的，空气将会更新鲜。little少的，形容词，其比较级是less，修饰不可数名词，few几乎没有，形容词，其比较级是fewer，更少，修饰可数名词，people，可数名词，用fewer修饰，air pollution，空气污染，不可数名词，用less修饰，故选D。 【点评】考查形容词的辨析。注意less和fewer意思和用法。 4．—Guess what? The university has accepted my application! —Wow! That's ________ new I've heard this year, Boris! Let's celebrate. A. a worse B. the worst C. a better D. the best 【答案】 D 【解析】【分析】句意：——猜猜什么？那所大学已经接受我的申请了。——哇喔，那是今年我听到的最好的消息，Boris，让我们庆祝一下。A.一个更糟的，比较级；B.最糟的，最高级；C.一个更好的，比较级；D.最好的，最高级。因为大学接受申请了，所以是好消息，排除A、B。根据 I've heard this year，今年我听到的，可知是最高级，故选D。 【点评】考查形容词辨析，注意平时识记最高级结构，理解句意。
现在进行时的用法
现在进行时用法 一、定义：1、表示说话时正在进行的动作及行为2、表示现阶段正在进行的动作。 二、结构:现在进行时常有三种句型： （1）肯定式：主语＋be＋v-ing＋其它。如： He is mending his bike．他正在修自行车。 （2）否定式：主语＋be＋not＋v-ing＋其它。如： He is not（isn't） mending his bike．他没在修自行车。 （3）疑问式：主要分一般疑问句和特殊疑问句两种句式。 一般疑问句：Be＋主语＋v-ing＋其它？如： —Is he mending his bike？他正在修自行车吗？—Yes，he is．（No，he isn't．） 特殊疑问句：疑问词＋be＋主语＋v-ing＋其它？如： —What is he doing？他正在干什么？ 三、何时用现在进行时？ （1）以Look！或Listen！开头的句子提示我们说话时动作正在进行，应用现在进行时。如： Look！The children are playing games over there． Listen！Who's singing in the classroom？ （2）当句子中有now（现在）时，常表示说话时动作正在进行，这时也常用现在进行时。如：We are reading English now． （3）描述图片中的人物的动作时常用现在进行时，以示生动。如： Look at the picture．The girl is swimming．（4）表示当前一段时间内的活动或现阶段正在进行的动作时常用现在进行时。这时常与时间状语these days，this week等连用。如：