A&B&C&D条款区别的解读

α和an的用法口诀
在英语中，α和an是两个常见的字母，它们可以作为单词的开头字母。

虽然这两个字母的发音和用法有些相似，但它们在使用上还是有一些区别的。

下面是一些关于α和an的用法口诀，帮助你更好地掌握它们的用法。

1.“元音前用an，辅音前用a。

”
这个口诀可以帮助你判断在哪个单词前使用α或an。

一般来说，如果单词的首字母是元音音素，那么应该使用an；如果单词的首字母是辅音音素，那么应该使用a。

例如，“an hour”（一个小时）、“a book”（一本书）。

2.“特定词后用an，普通词后用a。

”
这个口诀可以帮助你判断在哪个单词后使用α或an。

一般来说，在某些特定的单词后面需要使用an，比如单数形式的可数名词。

这些特定的单词大多数以元音音素开头，如“an orange”（一个橙子）、“an elephant”（一只大象）。

而在其他普通的单词后面需要使用a，如“a car”（一辆车）、“a cat”（一只猫）。

3.“u前用an，其他都用a。

”
这个口诀可以帮助你判断在哪个单词前使用α或an。

一般来说，在u前的单词需要使用an，如“an underwater world”（一个水下世界）。

而在其他情况下，如“a university”（一所大学）、“a unicorn”（一只独角兽），则使用a。

以上就是关于α和an的用法口诀，希望能够帮助你更好地掌握它们的用法。

当然，在实际使用中，还需要结合具体的语境和单词的含义来判断应该使用哪个字母。

a在英语中代表什么词性在英语中，字母"a"可以代表以下几种不同的词性：1. 作为冠词作为冠词时，"a"表示不定冠词，用于指代一类人或事物的其中一个，相当于汉语中的"一个"。

例如：a book（一本书）、a boy（一个男孩）。

2. 作为代词作为代词时，"a"可以表示"一个"或"一些"，用来代替特定的人或事物。

例如：Give me a pen（给我一支笔）、I saw a few birds in the sky （我看到了几只鸟在天上）。

3. 作为形容词作为形容词时，"a"表示"一个"或"一种"，用来修饰名词。

例如：abig house（一座大房子）、a beautiful flower（一朵美丽的花）。

4. 作为副词作为副词时，"a"可以表示"以某种方式"或"在某种程度上"。

例如：He walked a mile（他走了一英里）、I feel a little tired（我感觉有点累）。

5. 作为介词作为介词时，"a"表示"在...旁边"或"朝向...的方向"。

例如：He stooda tree（他站在一棵树旁边）。

6. 作为连词作为连词时，"a"表示"和"或"及"，用于连接两个相类似的事物。

例如：apples and oranges（苹果和橙子）。

总结起来，字母"a"在英语中可以充当不同的词性，包括冠词、代词、形容词、副词、介词和连词。

具体它所代表的词性，取决于其在句子中的具体语境和用法。

a的四个声调写法中文是一门声调语言，声调是指在发音时声音的高低起伏。

汉语中的声调有四个，即平声、上声、去声和入声。

在拼音中，每个汉字都标有一个声调符号，以表示其声调。

而在拼音中，a字母也有四个声调，因此我们称之为“a的四个声调写法”。

第一种写法：āā是a字母的第一声，也是最常见的一个声调。

它的发音是高声平调，类似于英语中的“ah”。

在汉语中，ā的发音比较柔和，不会像英语中的“ah”那样太尖锐。

例如，爸爸的拼音就是bàba，其中的第一个字母a就是ā的发音。

第二种写法：áá是a字母的第二声，它的发音是由低变高，然后再降下来，类似于英语中的“aw”。

在汉语中，á的发音比较尖锐，有些像“啊”的发音。

例如，妈妈的拼音就是māma，其中的第一个字母a就是á的发音。

第三种写法：ǎǎ是a字母的第三声，它的发音是由低变高，然后保持在一个较高的音调上，类似于英语中的“uh”。

在汉语中，ǎ的发音比较轻松，有些像“呀”的发音。

例如，姐姐的拼音就是jiějie，其中的第一个字母a就是ǎ的发音。

第四种写法：àà是a字母的第四声，它的发音是由低到高，然后降下来，类似于英语中的“ahh”。

在汉语中，à的发音比较沉重，有些像“啊”的发音。

例如，爷爷的拼音就是yéye，其中的第一个字母a就是à的发音。

总结a的四个声调写法在汉语中使用非常广泛，因为a字母在汉语中出现的频率也很高。

掌握这四个声调的发音，可以帮助我们更准确地发音，更好地理解和使用汉语。

同时，我们也应该注意到，不同的声调在不同的语境中可能会有不同的发音，因此我们需要不断地练习和学习，才能更好地掌握汉语的声调。

a在数学中的含义
在数学中，字母“a”通常有几种不同的含义，具体取决于上下文。

1.变量：字母“a”通常被用作变量，可以代表各种不同的值。

例如，在代数表
达式中，“a”可能代表一个系数、一个变量或者一个未知数。

2.常数：在某些情况下，“a”可能被用作常数。

常数是指不会改变其值的数，
如0、1或2等。

3.已知量：在解决问题时，“a”也可能被用作已知量，与未知数一起出现。

4.参数：在函数、方程或模型中，“a”也可能被用作参数。

参数是描述变量之
间关系的值，可以改变函数的形状、大小或其他特性。

5.幂的底数：在指数运算中，“a”也可以被用作幂的底数，与指数n一起表示
为“a^n”。

“a”在数学中的具体含义取决于上下文和用途。

在不同的领域和情况下，字母“a”可能具有不同的解释和用途。

1/ 1。

Features Array•Incorporates the ARM7TDMI® ARM® Thumb® Processor–High-performance 32-bit RISC Architecture–High-density 16-bit Instruction Set–Leader in MIPS/Watt–EmbeddedICE™ In-circuit Emulation, Debug Communication Channel Support •Internal High-speed Flash–512 Kbytes (AT91SAM7S512) Organized in Two Contiguous Banks of 1024 Pages of 256 Bytes (Dual Plane)–256 Kbytes (AT91SAM7S256) Organized in 1024 Pages of 256 Bytes (Single Plane) –128 Kbytes (AT91SAM7S128) Organized in 512 Pages of 256 Bytes (Single Plane) –64 Kbytes (AT91SAM7S64) Organized in 512 Pages of 128 Bytes (Single Plane) –32 Kbytes (AT91SAM7S321/32) Organized in 256 Pages of 128 Bytes (Single Plane)–16 Kbytes (AT91SAM7S161/16 Organized in 256 Pages of 64 Bytes (Single Plane) –Single Cycle Access at Up to 30 MHz in Worst Case Conditions–Prefetch Buffer Optimizing Thumb Instruction Execution at Maximum Speed–Page Programming Time: 6 ms, Including Page Auto-erase, Full Erase Time: 15 ms –10,000 Write Cycles, 10-year Data Retention Capability, Sector Lock Capabilities, Flash Security Bit–Fast Flash Programming Interface for High Volume Production•Internal High-speed SRAM, Single-cycle Access at Maximum Speed–64 Kbytes (AT91SAM7S512/256)–32 Kbytes (AT91SAM7S128)–16 Kbytes (AT91SAM7S64)–8 Kbytes (AT91SAM7S321/32)–4 Kbytes (AT91SAM7S161/16)•Memory Controller (MC)–Embedded Flash Controller, Abort Status and Misalignment Detection•Reset Controller (RSTC)–Based on Power-on Reset and Low-power Factory-calibrated Brown-out Detector –Provides External Reset Signal Shaping and Reset Source Status•Clock Generator (CKGR)–Low-power RC Oscillator, 3 to 20 MHz On-chip Oscillator and one PLL•Power Management Controller (PMC)–Software Power Optimization Capabilities, Including Slow Clock Mode (Down to 500 Hz) and Idle Mode–Three Programmable External Clock Signals•Advanced Interrupt Controller (AIC)–Individually Maskable, Eight-level Priority, Vectored Interrupt Sources–Two (AT91SAM7S512/256/128/64/321/161) or One (AT91SAM7S32/16) ExternalInterrupt Source(s) and One Fast Interrupt Source, Spurious Interrupt Protected •Debug Unit (DBGU)–2-wire UART and Support for Debug Communication Channel interrupt,Programmable ICE Access Prevention–Mode for General Purpose 2-wire UART Serial Communication•Periodic Interval Timer (PIT)–20-bit Programmable Counter plus 12-bit Interval Counter•Windowed Watchdog (WDT)–12-bit key-protected Programmable Counter–Provides Reset or Interrupt Signals to the System26175GS–ATARM–24-Dec-08AT91SAM7S Series Summary–Counter May Be Stopped While the Processor is in Debug State or in Idle Mode •Real-time Timer (RTT)–32-bit Free-running Counter with Alarm –Runs Off the Internal RC Oscillator•One Parallel Input/Output Controller (PIOA)–Thirty-two (AT91SAM7S512/256/128/64/321/161) or twenty-one (AT91SAM7S32/16) Programmable I/O Lines Multiplexed with up to Two Peripheral I/Os–Input Change Interrupt Capability on Each I/O Line–Individually Programmable Open-drain, Pull-up resistor and Synchronous Output•Eleven (AT91SAM7S512/256/128/64/321/161) or Nine (AT91SAM7S32/16) Peripheral DMA Controller (PDC) Channels •One USB 2.0 Full Speed (12 Mbits per Second) Device Port (Except for the AT91SAM7S32/16).–On-chip Transceiver, 328-byte Configurable Integrated FIFOs •One Synchronous Serial Controller (SSC)–Independent Clock and Frame Sync Signals for Each Receiver and Transmitter –I²S Analog Interface Support, Time Division Multiplex Support–High-speed Continuous Data Stream Capabilities with 32-bit Data Transfer•Two (AT91SAM7S512/256/128/64/321/161) or One (AT91SAM7S32/16) Universal Synchronous/Asynchronous Receiver Transmitters (USART)–Individual Baud Rate Generator, IrDA ® Infrared Modulation/Demodulation–Support for ISO7816 T0/T1 Smart Card, Hardware Handshaking, RS485 Support –Full Modem Line Support on USART1 (AT91SAM7S512/256/128/64/321/161)•One Master/Slave Serial Peripheral Interface (SPI)–8- to 16-bit Programmable Data Length, Four External Peripheral Chip Selects •One Three-channel 16-bit Timer/Counter (TC)–Three External Clock Input and Two Multi-purpose I/O Pins per Channel (AT91SAM7S512/256/128/64/321/161)–One External Clock Input and Two Multi-purpose I/O Pins for the first Two Channels Only (AT91SAM7S32/16) –Double PWM Generation, Capture/Waveform Mode, Up/Down Capability •One Four-channel 16-bit PWM Controller (PWMC)•One Two-wire Interface (TWI)–Master Mode Support Only, All Two-wire Atmel EEPROMs and I 2C Compatible Devices Supported (AT91SAM7S512/256/128/64/321/32)–Master, Multi-Master and Slave Mode Support, All Two-wire Atmel EEPROMs and I 2C Compatible Devices Supported (AT91SAM7S161/16)•One 8-channel 10-bit Analog-to-Digital Converter, Four Channels Multiplexed with Digital I/Os •SAM-BA ™ Boot Assistant –Default Boot program–Interface with SAM-BA Graphic User Interface •IEEE ® 1149.1 JTAG Boundary Scan on All Digital Pins•5V-tolerant I/Os, including Four High-current Drive I/O lines, Up to 16 mA Each (AT91SAM7S161/16 I/Os Not 5V-tolerant)•Power Supplies–Embedded 1.8V Regulator, Drawing up to 100 mA for the Core and External Components–3.3V or 1.8V VDDIO I/O Lines Power Supply, Independent 3.3V VDDFLASH Flash Power Supply –1.8V VDDCORE Core Power Supply with Brown-out Detector•Fully Static Operation: Up to 55 MHz at 1.65V and 85⋅C Worst Case Conditions•Available in 64-lead LQFP Green or 64-pad QFN Green Package (AT91SAM7S512/256/128/64/321/161) and 48-lead LQFP Green or 48-pad QFN Green Package (AT91SAM7S32/16)36175GS–ATARM–24-Dec-08AT91SAM7S Series Summary1.DescriptionAtmel’s AT91SAM7S is a series of low pincount Flash microcontrollers based on the 32-bit ARM RISC processor. It features a high-speed Flash and an SRAM, a large set of peripherals, includ-ing a USB 2.0 device (except for the AT91SAM7S32 and AT91SAM7S16), and a complete set of system functions minimizing the number of external components. The device is an ideal migration path for 8-bit microcontroller users looking for additional performance and extended memory.The embedded Flash memory can be programmed in-system via the JTAG-ICE interface or via a parallel interface on a production programmer prior to mounting. Built-in lock bits and a secu-rity bit protect the firmware from accidental overwrite and preserves its confidentiality.The AT91SAM7S Series system controller includes a reset controller capable of managing the power-on sequence of the microcontroller and the complete system. Correct device operation can be monitored by a built-in brownout detector and a watchdog running off an integrated RC oscillator.The AT91SAM7S Series are general-purpose microcontrollers. Their integrated USB Device port makes them ideal devices for peripheral applications requiring connectivity to a PC or cellu-lar phone. Their aggressive price point and high level of integration pushes their scope of use far into the cost-sensitive, high-volume consumer market.1.1Configuration Summary of the AT91SAM7S512, AT91SAM7S256, AT91SAM7S128, AT91SAM7S64, AT91SAM7S321, AT91SAM7S32, AT91SAM7S161 and AT91SAM7S16The AT91SAM7S512, AT91SAM7S256, AT91SAM7S128, AT91SAM7S64, AT91SAM7S321, AT91SAM7S32, AT91SAM7S161 and AT91SAM7S16 differ in memory size, peripheral set and package. Table 1-1 summarizes the configuration of the six devices.Except for the AT91SAM7S32/16, all other AT91SAM7S devices are package and pinout compatible.Notes: 1.Fractional Baud Rate.2.Full modem line support on USART1.3.Only two TC channels are accessible through the PIO.Table 1-1.Configuration SummaryDevice Flash TWI FlashOrganization SRAM USBDevicePort USART External Interrupt SourcePDC Channels TC Channels I/O 5V Tolerant I/O Lines Package A T91SAM7S512512 Kbytes Master dual plane 64 Kbytes 12(1) (2)2113Y es 32LQFP/QFN 64A T91SAM7S256256 Kbytes Master single plane 64 Kbytes 12(1) (2)2113Y es 32LQFP/ QFN 64A T91SAM7S128128 Kbytes Master single plane 32 Kbytes 12(1) (2)2113Y es 32LQFP/ QFN 64A T91SAM7S6464 Kbytes Master single plane 16 Kbytes 12(2)2113Y es 32LQFP/ QFN 64A T91SAM7S32132 Kbytes Master single plane 8 Kbytes 12(2)2113Y es 32LQFP/ QFN 64A T91SAM7S3232 Kbytes Master single plane 8 Kbytes notpresent 1193(3)Y es 21LQFP/ QFN 48A T91SAM7S16116 Kbytes Master/ Slave single plane 4 Kbytes 12(2)2113No 32LQFP A T91SAM7S1616 KbytesMaster/ Slavesingle plane4 Kbytesnotpresent1193(3)No21LQFP/ QFN 4846175GS–ATARM–24-Dec-08AT91SAM7S Series Summary2.Block DiagramFigure 2-1.AT91SAM7S512/256/128/64/321/161 Block Diagram56175GS–ATARM–24-Dec-08AT91SAM7S Series SummaryFigure 2-2.AT91SAM7S32/16 Block Diagram66175GS–ATARM–24-Dec-08AT91SAM7S Series Summary3.Signal DescriptionTable 3-1.Signal Description ListSignal NameFunctionTypeActive LevelCommentsPowerVDDIN Voltage and ADC Regulator Power Supply InputPower 3.0 to 3.6V VDDOUT Voltage Regulator Output Power 1.85V nominal VDDFLASH Flash Power Supply Power 3.0V to 3.6VVDDIO I/O Lines Power Supply Power 3.0V to 3.6V or 1.65V to 1.95V VDDCORE Core Power Supply Power 1.65V to 1.95V VDDPLL PLL Power 1.65V to 1.95VGND GroundGroundClocks, Oscillators and PLLsXIN Main Oscillator Input Input XOUT Main Oscillator Output Output PLLRC PLL FilterInput PCK0 - PCK2Programmable Clock Output OutputICE and JTAGTCK Test Clock Input No pull-up resistor TDI Test Data In Input No pull-up resistorTDO Test Data Out Output TMS Test Mode Select Input No pull-up resistor JTAGSELJTAG SelectionInputPull-down resistor (1)Flash MemoryERASEFlash and NVM Configuration Bits Erase CommandInputHighPull-down resistor (1)Reset/TestNRST Microcontroller Reset I/O Low Open-drain with pull-Up resistor TST Test Mode Select InputHighPull-down resistor (1)Debug UnitDRXD Debug Receive Data Input DTXD Debug Transmit DataOutput AICIRQ0 - IRQ1External Interrupt Inputs Input IRQ1 not present on AT91SAM7S32/16FIQFast Interrupt InputInputPIOP A0 - P A31Parallel IO Controller A I/OPulled-up input at resetP A0 - P A20 only on AT91SAM7S32/1676175GS–ATARM–24-Dec-08AT91SAM7S Series SummaryUSB Device PortDDM USB Device Port Data - Analog not present on AT91SAM7S32/16DDP USB Device Port Data +Analognot present on AT91SAM7S32/16USARTSCK0 - SCK1Serial Clock I/O SCK1 not present on AT91SAM7S32/16TXD0 - TXD1Transmit Data I/O TXD1 not present on AT91SAM7S32/16RXD0 - RXD1 Receive Data Input RXD1 not present on AT91SAM7S32/16RTS0 - RTS1Request T o Send Output RTS1 not present on AT91SAM7S32/16CTS0 - CTS1Clear T o Send Input CTS1 not present on AT91SAM7S32/16DCD1Data Carrier Detect Input not present on AT91SAM7S32/16DTR1Data Terminal Ready Output not present on AT91SAM7S32/16DSR1Data Set Ready Input not present on AT91SAM7S32/16RI1Ring Indicator Inputnot present on AT91SAM7S32/16Synchronous Serial ControllerTD Transmit Data Output RD Receive Data Input TK Transmit Clock I/O RK Receive Clock I/O TF Transmit Frame Sync I/O RFReceive Frame SyncI/OTimer/CounterTCLK0 - TCLK2External Clock Inputs Input TCLK1 and TCLK2 not present on AT91SAM7S32/16TIOA0 - TIOA2I/O Line A I/O TIOA2 not present on AT91SAM7S32/16TIOB0 - TIOB2I/O Line B I/OTIOB2 not present on AT91SAM7S32/16PWM ControllerPWM0 - PWM3PWM ChannelsOutput SPIMISO Master In Slave Out I/O MOSI Master Out Slave In I/O SPCK SPI Serial ClockI/O NPCS0SPI Peripheral Chip Select 0I/O Low NPCS1-NPCS3SPI Peripheral Chip Select 1 to 3OutputLowTable 3-1.Signal Description List (Continued)Signal Name FunctionTypeActive LevelComments86175GS–ATARM–24-Dec-08AT91SAM7S Series SummaryNote:1.Refer to Section 6. “I/O Lines Considerations” on page 14.Two-Wire InterfaceTWD Two-wire Serial Data I/O TWCK Two-wire Serial Clock I/OAnalog-to-Digital ConverterAD0-AD3Analog Inputs Analog Digital pulled-up inputs at reset AD4-AD7Analog Inputs Analog Analog InputsADTRG ADC Trigger Input ADVREFADC Reference AnalogFast Flash Programming InterfacePGMEN0-PGMEN2Programming Enabling Input PGMM0-PGMM3Programming Mode Input PGMD0-PGMD15Programming Data I/O PGMD0-PGMD7 only on A T91SAM7S32/16PGMRDY Programming Ready Output High PGMNVALID Data Direction Output Low PGMNOE Programming Read Input LowPGMCK Programming Clock Input PGMNCMD Programming CommandInputLow Table 3-1.Signal Description List (Continued)Signal Name FunctionTypeActive LevelComments96175GS–ATARM–24-Dec-08AT91SAM7S Series Summary4.Package and PinoutThe AT91SAM7S512/256/128/64/321 are available in a 64-lead LQFP or 64-pad QFN package.The AT91SAM7S161 is available in a 64-Lead LQFP package.The AT91SAM7S32/16 are available in a 48-lead LQFP or 48-pad QFN package.4.164-lead LQFP and 64-pad QFN Package OutlinesFigure 4-1 and Figure 4-2 show the orientation of the 64-lead LQFP and the 64-pad QFN pack-age. A detailed mechanical description is given in the section Mechanical Characteristics of the full datasheet.Figure 4-1.64-lead LQFP Package (Top View)Figure 4-2.64-pad QFN Package (Top View)106175GS–ATARM–24-Dec-08AT91SAM7S Series Summary4.264-lead LQFP and 64-pad QFN PinoutNote:1.The bottom pad of the QFN package must be connected to ground.Table 4-1.AT91SAM7S512/256/128/64/321/161 Pinout (1)1ADVREF 17GND 33TDI 49TDO 2GND 18VDDIO 34P A6/PGMNOE 50JTAGSEL 3AD419P A16/PGMD435P A5/PGMRDY 51TMS 4AD520P A15/PGMD336P A4/PGMNCMD 52P A315AD621P A14/PGMD237P A27/PGMD1553TCK 6AD722P A13/PGMD138P A2854VDDCORE 7VDDIN 23P A24/PGMD1239NRST 55ERASE 8VDDOUT 24VDDCORE 40TST 56DDM 9P A17/PGMD5/AD025P A25/PGMD1341P A2957DDP 10P A18/PGMD6/AD126P A26/PGMD1442P A3058VDDIO 11P A21/PGMD927P A12/PGMD043P A359VDDFLASH12VDDCORE 28P A11/PGMM344P A2/PGMEN260GND 13P A19/PGMD7/AD229P A10/PGMM245VDDIO 61XOUT 14P A22/PGMD1030P A9/PGMM146GND 62XIN/PGMCK 15P A23/PGMD1131P A8/PGMM047P A1/PGMEN163PLLRC 16P A20/PGMD8/AD332P A7/PGMNVALID48P A0/PGMEN064VDDPLL116175GS–ATARM–24-Dec-08AT91SAM7S Series Summary4.348-lead LQFP and 48-pad QFN Package OutlinesFigure 4-3 and Figure 4-4 show the orientation of the 48-lead LQFP and the 48-pad QFN pack-age. A detailed mechanical description is given in the section Mechanical Characteristics of the full datasheet.Figure 4-3.48-lead LQFP Package (Top View)Figure 4-4.48-pad QFN Package (Top View)4.448-lead LQFP and 48-pad QFN PinoutNote:1.The bottom pad of the QFN package must be connected to ground.Table 4-2.AT91SAM7S32/16 Pinout (1)1ADVREF 13VDDIO 25TDI 37TDO 2GND 14P A16/PGMD426P A6/PGMNOE 38JTAGSEL 3AD415P A15/PGMD327P A5/PGMRDY 39TMS 4AD516P A14/PGMD228P A4/PGMNCMD40TCK 5AD617P A13/PGMD129NRST 41VDDCORE 6AD718VDDCORE 30TST 42ERASE 7VDDIN 19P A12/PGMD031P A343VDDFLASH8VDDOUT 20P A11/PGMM332P A2/PGMEN244GND 9P A17/PGMD5/AD021P A10/PGMM233VDDIO 45XOUT 10P A18/PGMD6/AD122P A9/PGMM134GND 46XIN/PGMCK 11P A19/PGMD7/AD223P A8/PGMM035P A1/PGMEN147PLLRC 12P A20/AD324P A7/PGMNVALID36P A0/PGMEN048VDDPLL126175GS–ATARM–24-Dec-08AT91SAM7S Series Summary5.Power Considerations5.1Power SuppliesThe AT91SAM7S Series has six types of power supply pins and integrates a voltage regulator, allowing the device to be supplied with only one voltage. The six power supply pin types are:•VDDIN pin. It powers the voltage regulator and the ADC; voltage ranges from 3.0V to 3.6V , 3.3V nominal.•VDDOUT pin. It is the output of the 1.8V voltage regulator.•VDDIO pin. It powers the I/O lines and the USB transceivers; dual voltage range issupported. Ranges from 3.0V to 3.6V , 3.3V nominal or from 1.65V to 1.95V , 1.8V nominal. Note that supplying less than 3.0V to VDDIO prevents any use of the USB transceivers.•VDDFLASH pin. It powers a part of the Flash and is required for the Flash to operate correctly; voltage ranges from 3.0V to 3.6V, 3.3V nominal.•VDDCORE pins. They power the logic of the device; voltage ranges from 1.65V to 1.95V, 1.8V typical. It can be connected to the VDDOUT pin with decoupling capacitor. VDDCORE is required for the device, including its embedded Flash, to operate correctly.During startup, core supply voltage (VDDCORE) slope must be superior or equal to 6V/ms.•VDDPLL pin. It powers the oscillator and the PLL. It can be connected directly to the VDDOUT pin.No separate ground pins are provided for the different power supplies. Only GND pins are pro-vided and should be connected as shortly as possible to the system ground plane.In order to decrease current consumption, if the voltage regulator and the ADC are not used, VDDIN, ADVREF, AD4, AD5, AD6 and AD7 should be connected to GND. In this case VDDOUT should be left unconnected.5.2Power ConsumptionThe AT91SAM7S Series has a static current of less than 60 µA on VDDCORE at 25°C, including the RC oscillator, the voltage regulator and the power-on reset. When the brown-out detector is activated, 20 µA static current is added.The dynamic power consumption on VDDCORE is less than 50 mA at full speed when running out of the Flash. Under the same conditions, the power consumption on VDDFLASH does not exceed 10 mA.5.3Voltage RegulatorThe AT91SAM7S Series embeds a voltage regulator that is managed by the System Controller.In Normal Mode, the voltage regulator consumes less than 100 µA static current and draws 100 mA of output current.The voltage regulator also has a Low-power Mode. In this mode, it consumes less than 25 µA static current and draws 1 mA of output current.Adequate output supply decoupling is mandatory for VDDOUT to reduce ripple and avoid oscil-lations. The best way to achieve this is to use two capacitors in parallel: one external 470 pF (or 1 nF) NPO capacitor must be connected between VDDOUT and GND as close to the chip as possible. One external 2.2 µF (or 3.3 µF) X7R capacitor must be connected between VDDOUT and GND.136175GS–ATARM–24-Dec-08AT91SAM7S Series SummaryAdequate input supply decoupling is mandatory for VDDIN in order to improve startup stability and reduce source voltage drop. The input decoupling capacitor should be placed close to the chip. For example, two capacitors can be used in parallel: 100 nF NPO and 4.7 µF X7R.5.4Typical Powering SchematicsThe AT91SAM7S Series supports a 3.3V single supply mode. The internal regulator is con-nected to the 3.3V source and its output feeds VDDCORE and the VDDPLL. Figure 5-1 shows the power schematics to be used for USB bus-powered systems.Figure 5-1.3.3V System Single Power Supply Schematic146175GS–ATARM–24-Dec-08AT91SAM7S Series Summary6.I/O Lines Considerations6.1JTAG Port PinsTMS, TDI and TCK are schmitt trigger inputs. TMS and TCK are 5-V tolerant, TDI is not. TMS, TDI and TCK do not integrate a pull-up resistor.TDO is an output, driven at up to VDDIO, and has no pull-up resistor.The JTAGSEL pin is used to select the JTAG boundary scan when asserted at a high level. The JTAGSEL pin integrates a permanent pull-down resistor of about 15 k Ω to GND, so that it can be left unconnected for normal operations.6.2Test PinThe TST pin is used for manufacturing test, fast programming mode or SAM-BA Boot Recovery of the AT91SAM7S Series when asserted high. The TST pin integrates a permanent pull-down resistor of about 15 k Ω to GND, so that it can be left unconnected for normal operations. To enter fast programming mode, the TST pin and the PA0 and PA1 pins should be tied high and PA2 tied to low.To enter SAM-BA Boot Recovery, the TST pin and the PA0, PA1 and PA2 pins should be tied high fo at least 10 seconds.Driving the TST pin at a high level while PA0 or PA1 is driven at 0 leads to unpredictable results.6.3Reset PinThe NRST pin is bidirectional with an open drain output buffer. It is handled by the on-chip reset controller and can be driven low to provide a reset signal to the external components or asserted low externally to reset the microcontroller. There is no constraint on the length of the reset pulse, and the reset controller can guarantee a minimum pulse length. This allows connection of a sim-ple push-button on the pin NRST as system user reset, and the use of the signal NRST to reset all the components of the system.The NRST pin integrates a permanent pull-up resistor to VDDIO.6.4ERASE PinThe ERASE pin is used to re-initialize the Flash content and some of its NVM bits. It integrates a permanent pull-down resistor of about 15 k Ω to GND, so that it can be left unconnected for nor-mal operations.6.5PIO Controller A Lines•All the I/O lines PA0 to PA31on AT91SAM7S512/256/128/64/321 (PA0 to PA20 on AT91SAM7S32) are 5V-tolerant and all integrate a programmable pull-up resistor.•All the I/O lines PA0 to PA31 on AT91SAM7S161 (PA0 to PA20 on AT91SAM7S16) are not 5V-tolerant and all integrate a programmable pull-up resistor.Programming of this pull-up resistor is performed independently for each I/O line through the PIO controllers.5V-tolerant means that the I/O lines can drive voltage level according to VDDIO, but can be driven with a voltage of up to 5.5V. However, driving an I/O line with a voltage over VDDIO while the programmable pull-up resistor is enabled will create a current path through the pull-up resis-156175GS–ATARM–24-Dec-08AT91SAM7S Series Summarytor from the I/O line to VDDIO. Care should be taken, in particular at reset, as all the I/O lines default to input with the pull-up resistor enabled at reset.6.6I/O Line Drive LevelsThe PIO lines PA0 to PA3 are high-drive current capable. Each of these I/O lines can drive up to 16 mA permanently.The remaining I/O lines can draw only 8 mA.However, the total current drawn by all the I/O lines cannot exceed 150 mA (100 mA for AT91SAM7S32/16).166175GS–ATARM–24-Dec-08AT91SAM7S Series Summary7.Processor and Architecture7.1ARM7TDMI Processor•RISC processor based on ARMv4T Von Neumann architecture–Runs at up to 55 MHz, providing 0.9 MIPS/MHz •Two instruction sets–ARM ® high-performance 32-bit instruction set –Thumb ® high code density 16-bit instruction set •Three-stage pipeline architecture–Instruction Fetch (F)–Instruction Decode (D)–Execute (E)7.2Debug and Test Features•Integrated EmbeddedICE ™ (embedded in-circuit emulator)–Two watchpoint units–Test access port accessible through a JTAG protocol –Debug communication channel •Debug Unit–Two-pinUART–Debug communication channel interrupt handling –Chip ID Register•IEEE1149.1 JT AG Boundary-scan on all digital pins7.3Memory Controller•Bus Arbiter–Handles requests from the ARM7TDMI and the Peripheral DMA Controller •Address decoder provides selection signals for–Three internal 1 Mbyte memory areas –One 256 Mbyte embedded peripheral area •Abort Status Registers–Source, Type and all parameters of the access leading to an abort are saved –Facilitates debug by detection of bad pointers •Misalignment Detector–Alignment checking of all data accesses –Abort generation in case of misalignment •Remap Command–Remaps the SRAM in place of the embedded non-volatile memory –Allows handling of dynamic exception vectors •Embedded Flash Controller–Embedded Flash interface, up to three programmable wait states176175GS–ATARM–24-Dec-08AT91SAM7S Series Summary–Prefetch buffer, buffering and anticipating the 16-bit requests, reducing the required wait states–Key-protected program, erase and lock/unlock sequencer –Single command for erasing, programming and locking operations –Interrupt generation in case of forbidden operation7.4Peripheral DMA Controller•Handles data transfer between peripherals and memories •Eleven channels: AT91SAM7S512/256/128/64/321/161•Nine channels: AT91SAM7S32/16–Two for each USART –Two for the Debug Unit–Two for the Serial Synchronous Controller –Two for the Serial Peripheral Interface –One for the Analog-to-digital Converter •Low bus arbitration overhead–One Master Clock cycle needed for a transfer from memory to peripheral –Two Master Clock cycles needed for a transfer from peripheral to memory •Next Pointer management for reducing interrupt latency requirements•Peripheral DMA Controller (PDC) priority is as follows (from the highest priority to the lowest):Receive DBGU Receive USART0Receive USART1Receive SSC Receive ADC Receive SPI Transmit DBGU Transmit USART0Transmit USART1Transmit SSC TransmitSPI186175GS–ATARM–24-Dec-08AT91SAM7S Series Summary8.Memories8.1AT91SAM7S512•512 Kbytes of Flash Memory, dual plane–2 contiguous banks of 1024 pages of 256 bytes–Fast access time, 30 MHz single-cycle access in Worst Case conditions –Page programming time: 6 ms, including page auto-erase –Page programming without auto-erase: 3 ms –Full chip erase time: 15 ms–10,000 write cycles, 10-year data retention capability –32 lock bits, protecting 32 sectors of 64 pages –Protection Mode to secure contents of the Flash •64 Kbytes of Fast SRAM–Single-cycle access at full speed8.2AT91SAM7S256•256 Kbytes of Flash Memory, single plane–1024 pages of 256 bytes–Fast access time, 30 MHz single-cycle access in Worst Case conditions –Page programming time: 6 ms, including page auto-erase –Page programming without auto-erase: 3 ms –Full chip erase time: 15 ms–10,000 write cycles, 10-year data retention capability –16 lock bits, protecting 16 sectors of 64 pages –Protection Mode to secure contents of the Flash •64 Kbytes of Fast SRAM–Single-cycle access at full speed8.3AT91SAM7S128•128 Kbytes of Flash Memory, single plane–512 pages of 256 bytes–Fast access time, 30 MHz single-cycle access in Worst Case conditions –Page programming time: 6 ms, including page auto-erase –Page programming without auto-erase: 3 ms –Full chip erase time: 15 ms–10,000 write cycles, 10-year data retention capability –8 lock bits, protecting 8 sectors of 64 pages –Protection Mode to secure contents of the Flash •32 Kbytes of Fast SRAM–Single-cycle access at full speed196175GS–ATARM–24-Dec-08AT91SAM7S Series Summary8.4AT91SAM7S64•64 Kbytes of Flash Memory, single plane–512 pages of 128 bytes–Fast access time, 30 MHz single-cycle access in Worst Case conditions –Page programming time: 6 ms, including page auto-erase –Page programming without auto-erase: 3 ms –Full chip erase time: 15 ms–10,000 write cycles, 10-year data retention capability –16 lock bits, protecting 16 sectors of 32 pages –Protection Mode to secure contents of the Flash •16 Kbytes of Fast SRAM–Single-cycle access at full speed8.5AT91SAM7S321/32•32 Kbytes of Flash Memory, single plane–256 pages of 128 bytes–Fast access time, 30 MHz single-cycle access in Worst Case conditions –Page programming time: 6 ms, including page auto-erase –Page programming without auto-erase: 3 ms –Full chip erase time: 15 ms–10,000 write cycles, 10-year data retention capability –8 lock bits, protecting 8 sectors of 32 pages –Protection Mode to secure contents of the Flash •8 Kbytes of Fast SRAM–Single-cycle access at full speed8.6AT91SAM7S161/16•16 Kbytes of Flash Memory, single plane–256 pages of 64 bytes–Fast access time, 30 MHz single-cycle access in Worst Case conditions –Page programming time: 6 ms, including page auto-erase –Page programming without auto-erase: 3 ms –Full chip erase time: 15 ms–10,000 write cycles, 10-year data retention capability –8 lock bits, protecting 8 sectors of 32 pages –Protection Mode to secure contents of the Flash •4 Kbytes of Fast SRAM–Single-cycle access at full speed。

a_an所有用法你英语超好，怎么可以不知道a/an所有用法?今天给大家带来冠词a/an所有用法，希望能够给帮助到大家，下面就和大家分享，来欣赏一下吧。

你英语超好，怎么可以不知道a/an所有用法?冠词，在英语中运用无处不见，它分为定冠词，不定冠词。

一个普通名词前面经常会出现不定冠词a/an;如果，名词是属于特定名词，那么定冠词就使用the。

从今天开始，我们会详细谈一下冠词的使用方法~~首先要强调的是，不定冠词a/an表示泛指的概念，用法有以下几种：1.a/an+可数名词单数：通常表示数量“一”，泛指任意一个人或一件事，也可以表示一类人或事物。

例：This is an apple.这是一个苹果。

A dog is a faithful animal.狗是忠诚的动物。

2.a/an+表示人名的专有名词：是指表示“一个叫......的人”或“......式的人物”。

例：I want to be a Libai when I grow up.长大之后我想成为像李白一样的诗人。

A John called during your absence.你不在时一个叫John的人来过电话。

3.a/an+修饰语+表示季节，月份，日期，星期，三餐等的名词：泛指某个不确定的时间，“一顿......的饭”等。

例：The earthquake broke out in a July in last century.地震发生在上世纪的某个七月。

I had a big lunch yesterday.昨天我吃了一顿丰盛的午餐。

4.a/an+序数词：表示“另一，又一”。

例：I need a second cup of tea.我还需要一杯茶。

5.a/an+形容词最高级+可数名词单数：表示“一个很/非常......的......”。

例：He is a wisest man.他是个非常聪明的人。

6.a/an+抽象名词/物质名词(food,fruit,fog,rain,snow,wind等)：表示具体的人或事物，引起人们某种情绪的人或事物或表示“一......之意”。

a的8种发音音标的读法在英语中，字母"a"有8种不同的发音音标。

以下是它们的读法：1. /æ/音标：这个音标在单词中出现的频次最高，它发出较短的开口元音音频。

例如，在单词"cat"中，字母"a"的音标就是/æ/。

2. /ɑː/音标：这个音标表示一个长音的开口元音。

它通常出现在单词的重读音节中，例如在单词"car"中，字母"a"的音标就是/ɑː/。

3. /eɪ/音标：这个音标表示一个双元音，发音是由短音/ɛ/和长音/ɪ/组合而成。

例如，在单词"cake"中，字母"a"的音标就是/eɪ/。

4. /ɑ/音标：这个音标表示一个短而开口的后元音。

它通常在美式英语中出现，在单词"father"中，字母"a"的音标就是/ɑ/。

5. /ə/音标：这个音标表示一个中央中未阻塞的元音。

它通常出现在不重读的音节中，例如在单词"about"中，字母"a"的音标就是/ə/。

6. /ɔː/音标：这个音标表示一个长音的闭口后元音。

它通常出现在单词的重读音节中，例如在单词"born"中，字母"a"的音标就是/ɔː/。

7. /eə/音标：这个音标表示一个双元音，发音是由短音/ɛ/和后音/ə/组合而成。

例如，在单词"bear"中，字母"a"的音标就是/eə/。

8. /e/音标：这个音标表示一个短而闭口的前元音。

它通常出现在单词的非重读音节中，例如在单词"about"中，字母"a"的音标就是/e/。

需要注意的是，不同的单词和方言可能会有不同的发音音标。

上述的发音音标主要适用于英式英语，美式英语中有一些差异。

A如同汉字起源于象形，英文字母表中的每个字母一开始都是描摹某种动物或物体形状的图画，而这些图画最后演变成为符号。

但这些符号和原先被描摹之实物的形状几无相似之处。

谁也不能肯定这些象形字母原先究竟代表什么。

我们的解释只能是学者们基于史料作出的有根据的猜测。

一般认为希腊字母乃西方所有字母，包括拉丁字母的始祖。

其实希腊人的字母又是从腓尼基人那儿借过来的。

约在3000年前，在腓尼基字母表中字母A读如aleph，写起来形似字母V，中间再加一横，代表牛头或牛角，以后希腊人将它倒过来写。

对于古代腓尼基人来说，牛意味着财富，吃、穿、耕作都少不了它。

这也许就是A被列为第一个字母的缘故吧。

B和字母A一样，字母B也可以追溯到古代腓尼基。

在腓尼基字母表中B读作beth，代表房屋，在希伯来语中B也叫beth，也含房屋之意。

字母B原来形似原始社会的两室房屋，小写字母b是后来从大写字母B衍变出来的。

在今约旦河西岸有一犹太教、基督教圣地叫Bethlehem（伯利恒），该词至今还包含着beth这一成分。

B在字母表中之所以排在第二位也许是因为对人类的生存来说，住的重要性仅次于衣食。

（参见A）C字母C在腓尼基人的文字中叫gimel，代表骆驼。

它在字母表中的排列顺序和希腊字母Γ（gamma）相同，实际上其字形是从后者演变而来的。

C在罗马数字中表示100。

（参见A，G）DD在古时是描摹拱门或门的形状而成的象形符号，在古代腓尼基语和希伯来语中叫做daleth，是“门”的意思，相当于希腊字母Δ（delta）。

（参见A）EE是英文里用得最多的字母。

在腓尼基语和希伯来语中E是代表窗的象形符号，叫做he，相当于希腊字母Ε（epsilon）。

（参见A）FF为英文字母表中的第六个字母，源自腓尼基语的第六个象形字母，该字母形似今日之英文字母Y，代表木栓或木钉（peg），在腓尼基语和希伯来语的名称为waw。

中世纪重罪犯（felon）的左颊常被打上F的印记，以示惩戒。