HFAS11S伺服模塊，TOSHIBA數(shù)據(jù)庫
由于32位處理器的價(jià)格不斷下降，用戶已可以大量使用，而32位RISC處理器則更是受到青睞，并將在某些領(lǐng)域替代原來的8位單片機(jī)。其中，微處理器系列處于領(lǐng)先地位。筆者所介紹的數(shù)據(jù)采集系統(tǒng)中采用的是PHILIPS公司生產(chǎn)的以ARM7處理器作為內(nèi)核的LPC2104單片機(jī)。 1 MAX194簡(jiǎn)介
HFAS11S伺服模塊，TOSHIBA數(shù)據(jù)庫 MAX194是MAXIM公司推出的一種逐次逼近型模數(shù)轉(zhuǎn)換器(ADC)，具有高速、高精度、低功耗等特點(diǎn)。MAX194內(nèi)部設(shè)有校準(zhǔn)電路，用于保證全溫度范圍內(nèi)的線性度，從而維持全量程內(nèi)的高性能，且不需要外部的調(diào)整電路。分開的模擬和數(shù)字供電最大程度地減少了數(shù)字噪聲耦合。在轉(zhuǎn)換過程中，每轉(zhuǎn)換完成一個(gè)，數(shù)據(jù)位就輸出一位。此時(shí)，SCLK應(yīng)該接地，CLK既作為ADC的轉(zhuǎn)換時(shí)鐘又作為串行接口的移位輸出時(shí)鐘。
◇ 異步模式：?jiǎn)纹瑱C(jī)只能在MAX194完成一次轉(zhuǎn)換之后才能將轉(zhuǎn)換結(jié)果讀出，然后再啟動(dòng)下一次轉(zhuǎn)換。這種模式降低了MAX194連續(xù)轉(zhuǎn)換的速度。
1．3 硬件接口
串行接口標(biāo)準(zhǔn)與SPITM、QSPITM兼容。MAX194在進(jìn)行A/D轉(zhuǎn)換時(shí)需要由外部提供時(shí)鐘信號(hào)。圖2是MAX194與單片機(jī)采用異步模式的硬件連接圖。該圖中，MAX194進(jìn)行A/D轉(zhuǎn)換所需的時(shí)鐘信號(hào)由外部晶振分頻得到。使用者也可根據(jù)需要由單片機(jī)提供該時(shí)鐘信號(hào)。時(shí)鐘信號(hào)的最大頻率是1.7 MHz，參考電壓的范圍是0～VDDA+0.3 V。為了防止從AIN端輸入的信號(hào)損壞ADC，應(yīng)在信號(hào)輸入端加電壓限幅電路以保護(hù)MAX194。圖3是其時(shí)序圖。P3.0產(chǎn)生的START信號(hào)與CLK信號(hào)相“或”后作為啟動(dòng)轉(zhuǎn)換的CONV信號(hào)。CONV的下降沿可以啟動(dòng)轉(zhuǎn)換，開始轉(zhuǎn)換后監(jiān)測(cè)EOC，當(dāng)它由高電平變低時(shí)說明轉(zhuǎn)換已經(jīng)結(jié)束，適當(dāng)延時(shí)后就可以從串口讀出轉(zhuǎn)換結(jié)果，讀數(shù)據(jù)的最高速率是4.19 Mbps。其中后兩項(xiàng)是測(cè)試全顯電流和段電流的有效值。由于液晶屏的背電極和段電極之間是灌注了液晶材料的，因此在外加電壓驅(qū)動(dòng)下，可等效為一個(gè)電容性負(fù)載。所以，液晶屏的電流采樣電路是一個(gè)典型的微分電路，其輸出電壓是一個(gè)窄脈沖序列，使用RMS/DC轉(zhuǎn)換集成電路AD536A可以實(shí)時(shí)測(cè)試不同窄脈沖電壓的有效值。
1 液晶屏測(cè)試儀的系統(tǒng)組成
debugging, PLC programming software should be used first. These programming software can monitor the state of each variable and program diagram, which is the basic function, otherwise it cannot be debugged. For most slow and simple logic, the basic function of programming software is enough to complete the debugging task. If the logic is complex, spans many pages, or the signal changes quickly, it is very difficult to observe the real-time state with the naked eye and think logically. Most of the programming software will provide variable monitoring tables, put in all the variables that need to be concerned, and click monitoring to refresh the status in real time, which can solve the problem of monitoring a large number of variables to a certain extent. However, for programs with complex logic or fast change speed, we need to use the tool of sequence diagram to record the change process and analyze it slowly afterwards.Also, for the simple example of pump control above, if there is a phenomenon that the pump will occasionally stop before reaching the low liquid level after starting, what is the reason? It may be the jitter of the low liquid level signal, or the loose wiring of the output, etc. at this time, it is easy to judge if you can get the time sequence diagram at that time. If the sequence diagram is shown in Figure 2, we can judge that it is caused by the unreliability of the low liquid level signal. Just check the wiring of the low liquid level signal or the float switch. If the sequence diagram is shown in Figure 3, it is necessary to check the output wiring of the control command and the main circuit of the motor.
