HFAS11S伺服模塊，TOSHIBA數據庫
由于32位處理器的價格不斷下降，用戶已可以大量使用，而32位RISC處理器則更是受到青睞，并將在某些領域替代原來的8位單片機。其中，微處理器系列處于領先地位。筆者所介紹的數據采集系統中采用的是PHILIPS公司生產的以ARM7處理器作為內核的LPC2104單片機。 1 MAX194簡介
HFAS11S伺服模塊，TOSHIBA數據庫 MAX194是MAXIM公司推出的一種逐次逼近型模數轉換器(ADC)，具有高速、高精度、低功耗等特點。MAX194內部設有校準電路，用于保證全溫度范圍內的線性度，從而維持全量程內的高性能，且不需要外部的調整電路。分開的模擬和數字供電最大程度地減少了數字噪聲耦合。在轉換過程中，每轉換完成一個，數據位就輸出一位。此時，SCLK應該接地，CLK既作為ADC的轉換時鐘又作為串行接口的移位輸出時鐘。
◇ 異步模式：單片機只能在MAX194完成一次轉換之后才能將轉換結果讀出，然后再啟動下一次轉換。這種模式降低了MAX194連續轉換的速度。
1．3 硬件接口
串行接口標準與SPITM、QSPITM兼容。MAX194在進行A/D轉換時需要由外部提供時鐘信號。圖2是MAX194與單片機采用異步模式的硬件連接圖。該圖中，MAX194進行A/D轉換所需的時鐘信號由外部晶振分頻得到。使用者也可根據需要由單片機提供該時鐘信號。時鐘信號的最大頻率是1.7 MHz，參考電壓的范圍是0～VDDA+0.3 V。為了防止從AIN端輸入的信號損壞ADC，應在信號輸入端加電壓限幅電路以保護MAX194。圖3是其時序圖。P3.0產生的START信號與CLK信號相“或”后作為啟動轉換的CONV信號。CONV的下降沿可以啟動轉換，開始轉換后監測EOC，當它由高電平變低時說明轉換已經結束，適當延時后就可以從串口讀出轉換結果，讀數據的最高速率是4.19 Mbps。其中后兩項是測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，因此在外加電壓驅動下，可等效為一個電容性負載。所以，液晶屏的電流采樣電路是一個典型的微分電路，其輸出電壓是一個窄脈沖序列，使用RMS/DC轉換集成電路AD536A可以實時測試不同窄脈沖電壓的有效值。
1 液晶屏測試儀的系統組成
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.
