【正文】 4 前端數(shù)據(jù)采集 前端數(shù)據(jù)采集經(jīng)常做成模塊而且是典型地與 PC 機(jī)或控制器連接。前端數(shù)據(jù)采集在很多模型里都能運(yùn)行，包括 VXI 版本 ,如 Agilent E1419A 多功能測(cè)量和VXI 控制模型，雖然前端器成本已經(jīng)降低 ,但是這些系統(tǒng) 依然 會(huì)非常貴 ,除非你需要提供高的運(yùn)轉(zhuǎn) 能力 . 近些年隨著數(shù)據(jù)采集系統(tǒng)的廣泛應(yīng)用，人們對(duì)數(shù)據(jù)記錄儀的主 要技術(shù)指標(biāo)，如采樣頻率、分辨率、精度、控制方式、抗干擾能力、數(shù)據(jù)存儲(chǔ)容量及數(shù)據(jù)傳輸方式等方面都提出了越來(lái)越高的要求?？梢酝ㄟ^(guò)各種無(wú)線傳輸技術(shù)向外傳輸數(shù)據(jù)。出現(xiàn)了瞬態(tài)記錄的概念，超大容量的數(shù)據(jù)儲(chǔ)存空間已達(dá) 1TB。 參考資料 : [1]韓茜 .羅豐 .吳順君高速大容量固態(tài)存儲(chǔ)系統(tǒng)的設(shè)計(jì) [J]雷達(dá)科學(xué)與技術(shù) 2020(2) [2]沈沛 ,戈福慶 . 淺淡記錄儀的發(fā)展趨勢(shì) [J]. 中國(guó)儀器儀表 , 1998, (04) [3]金建祥，楊穎，郭豪杰，李杰 . 無(wú)紙記錄 儀 ──記錄儀發(fā)展新趨勢(shì) [J]. 工業(yè)儀表與自動(dòng)化裝置 , 1995, (04) 三、初步設(shè)計(jì)方法與實(shí)施方案 用戶通過(guò)鍵盤(pán)和顯示器設(shè)定系統(tǒng)時(shí)鐘，選擇所要啟動(dòng)的記錄通道，設(shè)定該通道的數(shù)據(jù) 量程 ，采集頻率和采集次數(shù)。得到對(duì)應(yīng)當(dāng)前數(shù)字量的實(shí)際物理值。在上位機(jī)上，通過(guò)軟件發(fā)送命令，可以隨時(shí)將已采集的數(shù)據(jù)傳送到上位機(jī)上。采用 U 盤(pán)作為存儲(chǔ)器， U 盤(pán)的好處在于其容量可變，不同大小的 U 盤(pán)所能儲(chǔ)存的數(shù)據(jù)量不同。 2 降低成本 此次所設(shè)計(jì)的數(shù)據(jù)記錄儀，采用單片機(jī)技術(shù)為核心技術(shù)，作為整個(gè)系統(tǒng)的中樞控制器，降低了一部分的制造成本。 四、預(yù)期結(jié)果 預(yù)期結(jié)果是完成一個(gè)具有多路數(shù)據(jù)采集的數(shù)據(jù)記錄儀，擁有至少三路的模擬量通道，可接受 05v 或 420mA 的信號(hào)輸入，并將數(shù)據(jù)進(jìn)行數(shù)模轉(zhuǎn)換后以 txt 格式儲(chǔ)存到U 盤(pán)中。 they can ignore the frame number and its CRC. If a function needs to track frame number, it must prehend both the PID and the time stamp. Fullspeed devices that have no particular need for bus timing information may ignore the SOF packet. Handshake Packets Handshake packets are used to report the status of a data transaction and can return values indicating successful reception of data, mand acceptance or rejection, flow control, and halt conditions. Only transaction types that support flow control can return handshakes. Handshakes are always returned in the handshake phase of a transaction and may be returned, instead of data, in the data phase. Handshake packets are delimited by an EOP after one byte of packet field. If a packet decodes as an otherwise valid handshake but does not terminate with an EOP after one byte, it must be considered invalid and ignored by the receiver. There are four types of handshake packets and one special handshake packet: indicates that the data packet was received without bit stuff or CRC errors over the data field and that the data PID was received correctly. ACK may be issued either when sequence bits match and the receiver can accept data or when sequence bits mismatch and the sender and receiver must resynchronize to each other. An ACK handshake is applicable only in transactions in which data has been transmitted and where a handshake is expected. ACK can be returned by the host for IN transactions and by a function for OUT, SETUP, or PING transactions. indicates that a function was unable to accept data from the host (OUT) or that a function has no data to transmit to the host (IN). NAK can only be returned by functions in the data phase of IN transactions or the handshake phase of OUT or PING transactions. The host can never issue NAK. NAK is used for flow control purposes to indicate that a function is temporarily unable to transmit or receive data, but will eventually be able to do so without need of host intervention. is returned by a function in response to an IN token or after the data phase 9 of an OUT or in response to a PING transaction. STALL indicates that a function is unable to transmit or receive data, or that a control pipe request is not supported. The state of a function after returning a STALL (for any endpoint except the default endpoint) is undefined. The host is not permitted to return a STALL under any condition. The STALL handshake is used by a device in one of two distinct occasions. The first case, known as “functional stall,” is when the Halt feature associated with the endpoint is set. A special case of the functional stall is the “manded stall.” Once a function?s endpoint is halted, the function must continue returning STALL until the condition causing the halt has been cleared through host intervention. Protocol stall is unique to control pipes. Protocol stall differs from functional stall in meaning and duration. A protocol STALL is returned during the Data or Status stage of a control transfer, and the STALL condition terminates at the beginning of the next control transfer (Setup). The remainder of this section refers to the general case of a functional stall. 2 Transaction Packet Sequences The packets that prise a transaction varies depending on the endpoint type. There are four endpoint types: bulk, control, interrupt, and isochronous. Batch transaction type were characterized by the error detection and retry way to ensure the host and function of data between the ponents of the ability to send errorfree. Flow control and hang in some conditions, the data phase handshake signals are replaced, resulting in two with no data transfer phase of the transaction. When the host is ready to receive a batch of data when it sends the input tag. Feature port through the return packet, or if unable to return data, NAK, or STALL handshake is returned as a response. NAK means the feature is temporarily unable to return data, and STALL be stopped permanently, said the port needs to USB system software intervention. If the host receives a legitimate data packets, then it uses ACK handshake to answer. If you receive data with the host detects an error, then it does not return handshake contracted out features. Control of transmission at least two transaction stages: the establishment and status. Transmission can be selectively controlled, including the establishment and status data between the stages of phase. In the establishment phase, the establishment of services for the features of the control port to transmit information. Establishment of issues in the format similar to the output, but the use of the building rather than the output of the PID. Building is always in the establishment of services relative to the use of data DATA0 PID. 10 Before the establishment of the functional ponents must accept the establishment of data and use ACK response, if the data is damaged, then discards the data and do not return to shake hands. Control the data transmission phase, if any, by mo